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The Florida Burrowing Owl in a Rural Enviro nment: Breeding Habitat, Dispersal, PostBreeding Habitat, Behavior, and Diet. By Robert Mrykalo A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Environmental Science and Policy College of Arts and Sciences University of South Florida Major Professor: Meli ssa M. Grigione, Ph.D. Ronald J. Sarno, Ph.D. Gordon A. Fox, Ph.D. Date of Approval: February 23, 2005 Keywords: Athene cunicularia floridana, sp ecies of special con cern, home range, avian ecology, telemetry Copyright 2005, Robert Mrykalo
Acknowledgements First, I would like to thank my dad a nd sisters for their love and support during these last few years. Next, I would like to thank my committee members, Dr. Melissa Grigione, Dr. Ron Sarno, and Dr. Gordon Fox, for their advice and comments during my thesis research and the writing of my thesis. I woul d especially like to thank Melissa and Ron for their advice, support, and friendship. One of the benefits of my graduate career was the opportunity to work and become friends with Melissa and Ron. I would like to thank Adam Cuppoletti for the use of his ATV during the latter part of my field research. Without the ATV I wouldnt have been able to conduct the radio telemetry portion of my thesis. I would like to thank Brian Mealey for his advice and field assistance. Also deserving a big thank you is Mr. and Mrs. Jim Strickland. Next, I would like to thank Nancy Richie for helping coordinate my field research on Marco Island. Fieldwork is fun, but it is a lot more fun when your friends are willing to help you or go with you into the field. Therefore, the following people deserve a huge thank you: Kelly Cupolletti, Lisa Fairchild, Dave Miller, Mark Muller, Jeanne Lambert, Emily Ferguson, Dharma Medina, Alicia Deoc han, Jason Hosford, and Kari Debofkey. A special thanks is due to Per Nixon for his non-stop positive attitude during our many long days in the field. He helped make the long hikes and overnight fieldwork enjoyable.
i Table of Contents List of Tables iii List of Figures iv Abstract vi Chapter One Burrowing Owl Habitat: Br eeding Habitat, Dispersal, and Post-Breeding Habitat. 1 Introduction 1 Breeding Habitat 2 Dispersal and Post-Breeding Habitat 4 Objectives 5 Methods 7 Locating Burrows 7 Radio Telemetry 9 Calculating Home Rang e and Dispersal Distance 12 Results 15 Attaching Transmitters 15 Home Range in Breeding Habitat 16 Flooding of Breeding Habitat 21 Dispersal and Post-Breeding Home Range 23 Discussion 26 Chapter Two Comparison of Diet and Potential Prey for Rural and Urban Burrowing Owls During the Breeding Period 31 Introduction 31 Methods 33 Results 36 Discussion 40 Insect Pitfall Traps 40 Small Mammal Traps 40 Burrow Mound 41 Pellet Analysis 41
ii Chapter Three Behavioral Observati ons of Adult and Juvenile Burrowing Owl during the Breeding Period 44 Introduction 44 Methods 46 Results 49 Adults with Young 49 Adults without Young 52 Juvenile Burrowing Owls 55 Discussion 57 Behavior 57 Location of Adult Burrowing Owls and Transition Probability 58 Chapter Four Evaluation of Three Methods to Capture Burrowing Owls in Florida 62 Introduction 62 Methods 64 Results 66 Discussion 67 References 68
iii List of Tables Table 1 Juvenile Burrowing Owls Fitted with Necklace Radio Transmitters 15 Table 2 Kernel Home Range Es timates in Breeding Habitat 16 Table 3 Evening Relocations of Juvenile Burrowing Owls 21 Table 4 Dispersal Distance of Juvenile Burrowing Owls 23 Table 5 Organisms Captured in Pitfall Traps at Marco Island 36 Table 6 Organisms Captured in Pitfall Traps at Rutland Ranch 36 Table 7 Marco Island: Analysis of Pellets and Remains Found on Burrows 38 Table 8 Rutland Ranch: Analysis of Pellets and Remains Found on Burrows 39 Table 9 Ethogram of Adult Burrowing Owl Behaviors 46 Table 10 Ethogram of Juveni le Burrowing Owl Behaviors 47 Table 11 Description of Adu lt Burrowing Owl Locations at Rutland Ranch 48 Table 12 Sum of Locations for Adult Owls during Five Minute Observation Periods 50 Table 13 Transition Probabilities for Adult Burrowing Owls Raising Young Versus Adults Not Raising Young 51 Table 14 Number of Owls Captur ed/Recaptured during Three Time Periods 66
iv List of Figures Figure 1 Location of Research Areas: Rutland Ranch and Marco Island 8 Figure 2 Location of All Active Burrows on Rutland Ranch 10 Figure 3 Roads Surveyed for Missing Burrowing Owls 13 Figure 4 Kernel Home Range Estimate for Frequency 151.470 MHz 17 Figure 5 Kernel Home Range Estimate for Frequency 151.530 MHz 18 Figure 6 Kernel Home Range Estimate for Frequency 151.665 MHz 19 Figure 7 Kernel Home Range Estimate for Frequency 151.690 MHz 20 Figure 8 Monthly Rainfall Amounts for Station 528 from 2000-2004 22 Figure 9 Daily Rainfall at Station 528 for July and August of 2004 22 Figure 10 Kernel Home Range Estimate for Frequency 151.530 MHz 25 Figure 11 Location of Transects, Pitf all Traps, and Small Mammal Traps Within Improved Pasture at Rutland Ranch 34 Figure 12 Prey Remains in Pellets from Marco Island and Rutland Ranch 37 Figure 13 Behavior of Adult Fema le Burrowing Owls Raising Young 49 Figure 14 Behavior of Adult Ma le Burrowing Owls Raising Young 49 Figure 15 Behavior of Adult Fema le Burrowing Owls Without Young 52 Figure 16 Behavior of Adult Ma le Burrowing Owls Without Young 53 Figure 17 Observation Periods (X) for Adult Burrowing Owls 54 Figure 18 Behavior of J uvenile Burrowing Owls 55
v Figure 19 Observation Periods (X) for Juvenile Burrowing Owls 56
vi The Florida Burrowing Owl in a Rural Enviro nment: Breeding Habitat, Dispersal, PostBreeding Habitat, Behavior, and Diet. Robert Mrykalo ABSTRACT The first observations of Florida burrowing owls ( Athene cunicularia floridana ) occurred in the 19th century on historical dr y prairie habitat in s outh central Florida. These early observations documented the ecology of burrowing owls in rural environments. Since then the vast majority of research on this subspecies has been undertaken in suburban and urban environmen ts during the breeding period. The research undertaken on burrowing owls in suburban a nd urban environments includes determining natal dispersal distance, assessing female fec undity, mate fidelity, territory fidelity, date of juvenile and adult dispersal from breeding habitat, date of clutch initiation, nesting success, density of breeding pairs, causes of mortality, prey pr eference, and minimum annual survival of fledglings, juveniles, a nd adults. Very little research has been undertaken on burrowing owls in rural environments. The purpose of this thesis was to eluc idate the behavior and ecology of burrowing owls in a rural environment. Th e topics researched in this thesis include home range in breeding habitat, dispersal distance to postbreeding habitat, location of post-breeding habitat, behavior during the breeding period, diet of rural versus urban owls, and the evaluation of three methods to trap burrowing owls. The results of this thesis indicate th at, during the daytime, juvenile burrowing owls utilized habitat very close to the ma in and satellite burrows during the breeding period. At night juvenile owls foraged in an extensive saw palmetto patch surrounding the breeding habitat. The predominant prey of both rural and urban burrowing owls during the breeding period was insects. Disp ersal of juvenile burrowing owls from breeding habitat coincided with the flooding of the breeding hab itat during the rainy
vii season. During the post-breeding period, juvenile burrowing owls shifted from colonial to solitary activity and utilized habitat consisting of saw palmetto and scrub oak. The location of adult burrowing owls in the impr oved pasture and their behavior during the breeding period depended on an owls sex and if it was or was not raising young.
1 Burrowing Owl Habitat: Breeding Habitat, Dispersal, and Post-Breeding Habitat. Introduction Early observations of burrowing owls ( Athene cunicularia floridana ) occurred on the dry prairie ecosystem occupying the s outh central portion of Florida (Cahoon 1885, Hoxie 1889, Rhoads, 1892, Scott 1892, Palmer 1896) The vegetative structure of dry prairie ecosystems varies from grassy areas of variable si ze interspersed within dense stands of saw palmetto ( Serenoa repens ) to expansive open areas containing a variety of grasses and sedges with scattered patches of trees and shrubs (Dav is 1943). In northern Florida, dry prairie ecosystems contain cabbage palm flatwo ods and also merge into wet flatwoods and pine flatwoods (Abrahamson and Hartnett 1990). Periodic natural fires due to lightning strikes and flooding may have ma intained the dry prairie ecosystem (Platt and Huffman 2004). Most lightni ng strikes occur during June to September (Abrahamson 1984a) and roughly 1,000 fires are set each year by lightning (Tanner et al. 1991). Highly flammable plants found within dry prairies, such as wiregrass ( Aristida stricta ) and saw palmetto, helped fuel these natural fires (A brahamson and Hartnett 1990). In turn, fire benefits native grass species of dry prai ries by increasing the rate of flowering (Abrahamson 1984b) and creating open areas de void of trees and shrubs thereby reducing the competition for resources such as wa ter, light, and nutrients (Abrahamson and Hartnett 1990). Periodic fires and flooding in dry prairies, coupled with natural firebreaks such as rivers and wetlands, may have created a con tinuously shifting mo saic of short grass habitat suitable for breeding burrowing owls Millsap (1997) hypothe sized that burrowing owls were nomadic and followed these short-te rm disturbances that created new breeding habitat.
2 Breeding Habitat Observations of burrowing owls on dry pr airies documented the unique ability of these owls to dig their own breeding and sa tellite burrows. Rhoads (1892) and Palmer (1896) located burrows excavated in mois t sand on short grass slopes interspersed between saw palmetto patches and the waters edge of swamps. Burrows have also been excavated in dry soils at the highest elevat ed areas of pasture c ontaining shrubs (Hoxie 1889, Scott 1892) and, in one instance, clumps of tall grass (Palmer 1896). The burrows, which can be 3-10 feet in length, contain an enlarged nest chamber at their terminus (Rhoads 1892, Scott 1892, Nicholson 1954, Sprunt 1954). A breeding pair of owls excavates one breeding burrow and one or more satellite burrows (Scott 1892, Neill 1954, Wesemann 1986, Mealey 1997). Both the in side and outside of the burrows are decorated with a variety of items including cow manure, horse manure, dog feces, grass, and refuse (Palmer 1896, Nicholson 1954, Mealey 1997). Male and female Florida burrowing owls can breed at one year of age (Haug et al. 1993). Breeding occurs between October and July with the majority of females laying eggs in the spring (Nicholson 1954, Course r 1976, Millsap and Bear 1990). Roughly 2-10 eggs are layed per nest (Rhoads 1892, Scott 1892, Nicholson 1954, Owre 1978, Stevenson and Anderson 1994). Females do a ll brooding of the young. Males initially do all of the hunting and provisioning of fema les while they are incubating. Females begin hunting when chicks are about two weeks old (Haug et al. 1993). There is no available information on the number of days before Florida burrowing owls fledge, but the Western burrowing owl fledges 44 days after hatching (Landry 1979). Rural breeding habitat varied in size from large expansive prairies to small open areas occupying only a few hectares (Bent 1938). Mr. N.B. Moore, in a correspondence to Ridgeway (1874), reports finding three comm unities of burrowing owls each separated by 1.2-1.6 kilometers. Each community contai ned 7-8 burrows. Rhoads (1892) located 23 owls in areas roughly 2.6 kilometers in size and one colony containing hundreds of pairs of burrowing owls stretching approximate ly 4.8 kilometers. On a large expanse of prairie approximately 32-48 kilometers wide and 80 kilometers long, Scott (1892) located
3 3-4 pairs of burrowing owls per 2.6 square kilo meters. Several kilometers of prairie were traversed before he would locate another small colony. Palmer (1896) observed colonies containing 3-6 burrows and the burrows se parated by 27-91 meters. The colonies he located were separated by many kilometers. Observations in the fall by Hoxie (1889) discovered small colonies containing 3-11 burrows. Much of the area comprising dry prairies has been lost due to development or has been converted to grazing pasture, agricu ltural land, or timber production (Birnhak and Crowder 1974, Abrahamson and Hartnett 1990). Anthropogenic changes to breeding habitat were already evident to Palmer (1896) when he noted that much of the prairie had been converted to grazing land and fires were often set by ranchers to burn off dead and undesirable vegetation. There is also evid ence of cattle trampling burrows (Rhoads 1892). New prairie-like breeding habitat has been created due to the continuous clearing and draining of previously unsuitable habitat (Neill 1954, Owre 1978, Courser 1979). Some of the new areas on which burrowing ow ls currently breed include grazing pastures (Mealey 1997), college campuses (Courser 1976), private residences (Mealey 1997), airports (Owre 1978, Mealey 1997), vacant lots (Wesemann 1986, Millsap and Bear 1990), borders of interstates (Owre 1978) a nd industrial parks (Courser 1976). These open, short grass areas mimic the original breeding habitat (Owre 1978, Wesemann 1986, Millsap and Bear 1997). Land clearing has resu lted in the expansion of breeding habitat north, northwest, south, and southeast of the orig inal dry prairies in central and southern Florida (MacKenzie 1944, Ne ill 1954, Ligon 1963, Hennemann 1980). Breeding habitat has been an important component of previous research on burrowing owls and has included determining na tal dispersal distance (Millsap and Bear 1997), assessing female fecundity (Millsap and Bear 2000), mate fidelity (Millsap and Bear 1997), territory fidelity (Mi llsap and Bear 1997), date of juvenile and adult dispersal from breeding habitat (Courser 1976), date of clutch initiation (C ourser 1976), nesting success (Mealey 1997, Millsap and Bear 2000), de nsity of breeding pairs (Millsap and Bear 1988), causes of mortality (M ealey 1997), prey preference (Lewis 1973, Hennemann 1980, Wesemann 1986), and minimum annual survival of fledglings,
4 juveniles, and adults (Mills ap and Bear 1997). The majority of previous research has been conducted in suburban or industrial areas. Few studies have been undertaken in ag ricultural areas, such as grazing land for cattle, and areas managed as natural habitat. The lack of research in these areas may be due to the lack of availabl e data regarding the distribu tion and abundance of burrowing owls in these areas throughout the state. Th ere have been recommendations to expand the monitoring of populations and also conduct a statewide inventory of the breeding populations in Florida (Owre 1978, Millsa p 1997). It wasnt until 1999 that a commendable statewide census was conducted on burrowing owls using data from historic and current owl sites. The lack of previous data on agricultural sites, coupled with reduced access to agricultural areas (Bow en 2000) plus the majority of ranchland surveys conducted from roads (Bowen 2004, personal communication) may have hindered the statewide census. Some state owne d lands managed as natural areas have not been surveyed for burrowing owls fu rther hindering the statewide census. Dispersal and Post-Breeding Habitat There is very little information on w hy some burrowing owls disperse from breeding habitat while others remain. Early observations indicated that burrowing owls disappeared at the end of the breeding season (Hoxie 1889, Bendire 1892). Nicholson (1954) noted that few owls were located on breeding habitat in winter. Burrows flood during the breeding period (Nicholson 1954, Mills ap and Bear 1988) and Mealey (1997) hypothesized that burrow flooding during the rainy season may be a proximate dispersal mechanism for burrowing owls. Subsequent observations of dispersal indicate that a small number of individuals in a metapopulation may disperse (Courser 197 6) or all individuals of a metapopulation may disperse (Stevenson and Anderson 1994, personal observation 2003, 2004). Stevenson and Anderson (1994) reported that of 11 relocated burrowing owls, five did not disperse, five dispersed 18 kilometers south, and one dispersed 74 kilometers north. Their results indicate that burrowing owls ma y undergo frequent pos t-breeding dispersal.
5 Sightings of burrowing owls have occurred in unusual areas such as 16 kilometers (Castenholz 1954) and 40 kilometers o ff the Florida coast (Ogden 1972). Florida Burrowing Owls have even been located outside of Florida including three occasions in New York (Davis 1977), and once in North Ca rolina (Sykes 1974) and Alabama (Howell 1928). The sightings of burrowing owls outside of Florida and the continued expansion of breeding range within the state (Li gon 1963, Courser 1979) suggest that dispersal distance can be noteworthy. The evidence of post-breeding di spersal indicates that postbreeding habitat may be an unknown but important component of burrowing owl ecology. The lack of information on post-breeding ha bitat may be due to the difficulty in locating this species after breeding. There have been several hypotheses proposed to explain why burrowing owls may be difficult to locate during the post-breeding period. First, their cryptic coloration and ability to blend in with the surrounding habit (Millsap 1997) may make it difficult to locate dur ing post-breeding periods. Second, burrowing owls may shift activity patte rns and become more crepus cular, nocturnal (Hoxie 1889, Mealey 2004, personal communication), a nd arboreal (Hoxie 1889) during the postbreeding period. Third, burrowing owls may disperse long distances to habitat that differs from breeding habitat. Any of these hypot heses or combination of hypotheses could explain the disappearance of burrowing owls during the post-breeding period. Objectives The objectives of this study were to 1) determine the home range of adult and juvenile burrowing owls in br eeding habitat, 2) measure j uvenile and adult dispersal distance from breeding habitat to post-breeding habitat, 3) locate post-breeding habitat, and 4) determine the home range of adult a nd juvenile burrowing ow ls in post-breeding habitat. Post-breeding habita t was defined as any habitat occupied by burrowing owls when main and satellite burrows were no longer utilized. The following hypotheses were to be tested:
6 Home range comparison : H O : Post-breeding home range for adult burrowing owls will not be significantly different in size from breeding home range. H 1 : Post-breeding home range will be sma ller because adults are only foraging for themselves and not for juvenile burrowing owls. Post-breeding habitat : H O : The vegetative structure of the post-breeding habitat will not be comparatively different from the breeding habitat. H 1 : Post-breeding habitat will be compara tively different from breeding habitat because adults are no longer reliant on shor t grass for excavating burrows, using these burrows to raise and protect juvenile owls, and detect predators.
7 Methods The study site was Rutland Ranch, in Br adenton, FL (Figure 1). Rutland Ranch encompasses approximately 2,372 hectares a nd is managed by the Southwest Florida Water Management District (Barnwell et al 2003). The ranch contains a mixture of habitats including oak scrub, herbaceous marshes, riparian hardwoods, pine flatwoods, and non-native pastures. The dominant soil types include Cassia, Duette, Myakka, Pomello, St. Johns, and Wave land fine sands (Barnwe ll et al. 2003). Vegetation associated with these soil types include sand pine ( Pinus clausa), live oak ( Quercus virginiana ), and saw palmetto (Barnwell et al 2003). Florida Burrowing Owls excavate burrows on an 81-hectare rectangular piece of improved pasture (Barnwell et al. 2003). The pasture is located at the followi ng UTM coordinates: Zone 17 0375665E and 3044342N. Locating Burrows The improved pasture was surveyed twice for active burrows: 3/26/04 and 7/10/04. The pasture was surveyed twice beca use, over time, burrows may be abandoned, destroyed by predators, and new burrows excavated by resident and immigrating burrowing owls. The survey began at the eas t side of the pasture. Three surveyors separated by 20 meters walked from the nor th end to the south end of the pasture scanning the ground for burrows. A burrow wa s identified as being excavated by burrowing owls if any one or more of the following conditions were met: insect remains were found at the burrow mound or entrance, owl feathers were found at the burrow mound or entrance, regurgitated pellets were found at the burrow m ound or entrance, or owls were sighted at or near the burrow. When the south end of the pasture was reached the three surveyors shifted 60 meters west a nd walked to the north end of the pasture. This process was repeated until the entire pasture was surveyed.
Legend Florida Counties Manatee County Collier County Rutland Ranch Marco Island 012525062.5Milesd Figure 1: Location of Research Areas on Rutland Ranch and Marco Islan Figure 1: Location of Research Areas: Rutland Ranch and Marco Island 8
9 A Garmin GPS model 12 CX was used to determine the loca tion of main and satellite burrows, for each pair of owls, and th e four corners of the improved pasture. The main burrow was distinguished from the satellite burrows by the male burrowing owl delivering food to the burrow occupied by the female, the female spending the majority of time in one burrow, and/or the presence of recently hatched chicks at the burrow entrance. Each GPS location was recorded using the UTM coordinate system and NAD27 datum. The location of each burrow was late r stored in a Microsoft Excel table. The tables were converted into dBASE IV fo rmat and imported into ArcMap 8.3. Each imported table was then converted into X, Y data, added to a layer in ArcMap 8.3, and then saved as a shape file. The location of the four corners of the past ure were also stored as a Microsoft Excel table, converted into the dBASE IV format, and imported into an ArcMap 8.3 layer using the same procedures for the burrows. The four corners of the improved pasture were converted into a polygon shape file using XTools. A digital raster graphic (DRG) containing Rutland Ranch, sca nned from a 7.5 minute topographic map of the Rye quadrate, was imported into ArcMap 8. 3 as a layer. The improved pasture shape file, burrow shape files, and DRG were used to create a map indi cating the position of each burrow, for each of the two time peri ods that we conducted surveys (Figure 2). Radio Telemetry Adult and juvenile bu rrowing owls were captured using noose carpet traps (Mealey 1997, Millsap and Bear 1997, Mehl et al. 2003) placed on the burrow mound and in the entrance of the burrows. Owls were captured on the burrow mound and also inside the entrance when exiting or enteri ng the burrow. The dependence of juvenile and adult burrowing owls on their main and sate llite burrows (Mealey 1997) allowed us to occasionally herd owls toward their burrows at which noose carpet traps were set. This was accomplished by walking around burrows until individual owls were located between research personal and a burrow and then slowly walking toward the owl. We stopped walking toward an owl when it fl ew at or near the trapped burrow.
!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(! (! (! (! (! (! (! (! (! (! (! (! (! (! (! ( Figure 2: Location of all Active Burrows on Rutland Ranch Legend!(All Main and Satellite Burrows 03/04! (All Main and Satellite Burrows 07/04 Improved Pasture 0220440110Meters 10
11 Captured owls were weighed to the near est gram by placing the owl in a cloth or plastic bag suspended from a 300 gram Peso la LightLine Spring Sc ale. The sexes of adult owls were identified by the presence or absence of a brood patch and feather coloration. Females had darker feathers a nd a conspicuous brood patch on their lower chest area (Martin 1973). The brood patc h was distinguished by de-feathering and thickening of the skin surface (Lea and Klandorf 2002). Male burrowing owls were identified by the lack of a brood patch and sun bleached lightening of feather coloration. The difference in feather color is due to ma les spending more time outside of the burrows searching for food in order to provision females during incubation (Martin 1973). Three to five chest feathers were removed from cap tured juvenile burrowing owls in order to sex individuals. The feathers were sent to a laboratory for DNA PCR analysis (Avian Biotech 2004). Captured adult and juvenile burrowing owls were fitted with necklace radio transmitters. The transmitters, non-scanning recei ver, and Yagi antenna, were made by AVM Instrument Company Limited. The frequency coverage for the receiver and transmitters was 151.000 151.999 MHz. The maximum range of the receiver and transmitters during field tests was 1.61 kilo meters. Five transmitters were randomly selected to determine the precision of directi onal bearings. Five bear ings were recorded for each transmitter, which had been placed in habitat similar to the improved pasture. The mean and standard deviation for the pr ecision of directional bearings was 1.64 4.13 degrees (White and Garrot 1990). The average weight of the transmitters was 4.9 grams. With an adult average weight of 150 grams (Millsap 1997) each transmitter weighed 3.3% of adult body weight. Each transmitter had an elastic collar covered with shrink wrap to reduce the possibility of abrasion. The elastic collar was spliced with a small piece of cotton string that would disintegrate over time and allow the transm itter to detach from the owl after the study was completed. When handling captured owls a cloth covering was temporarily placed over the owls head when it exhibited signs of stress such as tongue-snapping (Mealy 1997). An aba, a rectangular piece of cloth that holds the raptors wrists, was used to restrain owls (Maechtle 1998) when only one individual was handling owls and attaching
12 transmitters. After attaching a transmitter we observed an individual for several days in order to determine an owls affinity for wearing a transmitter. After a transmitter was attached an attempt was made to relocate an owl once each day in the improved pasture using a non-s canning receiver and a four-element Yagi antenna. Relocation attempts took place between 10 am and 8 pm. Two relocations were used to triangulate the lo cation of each owl during the breeding and post-breeding periods. During the evening of 8/01/04, hourly relocations were attempted between 9 pm and 5 am to document activity and locati on of each owl during the evening in the improved pasture. The date, time, transmitter frequency, UTM X and Y coordinates, signal bearing, and habitat type (urban, suburban, rural, or pasture) were recorded for both the day and evening relocations (White and Garrot 1990). Broad habitat types were utilized because there was no idea how far bu rrowing owls were capable of dispersing. Urban areas were characterized as city or industrial areas, suburban areas were characterized as residential ou tskirts of a city, rural areas were characterized as open areas with little or no development, and pasture was characterized as land used to graze cattle. The relocation data for each owl was saved in separate Excel tables and later converted into a dBASE IV table. All the available road and trails within Rutland Ranch were searched by ATV when any radio collared owl was not relo cated during the day and evening telemetry sessions. I would stop approximately every 100 meters and scan with the receiver and antenna for the missing frequency. If an owl was not located after several such attempts I then searched along the road network surroundi ng Rutland Ranch as displayed in Figure 3. I stopped every half mile and scanned with the receiver an d antenna. Finally, if an owl was still not located, aerial telemetry was attempted to locate the missing owls. Calculating Home Range and Dispersal Distance The computer program Location of a Si gnal 3.0.1 (LOAS) was used to calculate each owls location from the relocation da ta. The dBASE IV tables containing the relocations for each owl were imported into LOAS, the location for each owl calculated,
Duette Rd. SR 62 SR 64 CR 675 Figure 3: Roads Surveyed for Missing Burrowing Owls 0482Miles Legend Major Roads Surrounding Research Area Estimated Distance of Signal Reception Improved Pasture 13
14 and the location data for each owl was exported as a dBASE IV table. These tables were then imported into ArcMap 8.3, converted into X, Y data, added to a layer in ArcMap 8.3, and then saved as a shapefile. The ArcV iew extension Animal Movement V.2 Beta was used to calculate the home range for each owl. In Animal Movement V.2 Beta the fixed kernel home range estimate, with least squares cross validation as the smoothing pa rameter, was used to calculate the home range in the breeding and post-breeding periods. The ke rnel home range is a nonparametric method that calculates a probabil ity density estimate for the distribution of data points on a two dimensional plane. A pr obability density estimate, the kernel, is placed over each data point. The density estim ate for the distribution of data points is calculated by the proximity (ove rlap of kernels) of data points to themselves or a grid placed over the data set (Worton 1989, Seaman et al. 1998). The program calculated three separate home range estimates for each owl based on predetermined probabilities (95, 75, and 50%) of the estimated utilization distribution. The minimum convex polygon method to estimate home range was not utilized in this study because relocations in the peripherary of main activ ity can drastically affect the home range estimate. Also, this method does not indicate the inte nsity of habitat use (Harris et al. 1990). I defined dispersal as an owl moving fr om its breeding habita t in the improved pasture to any habitat outside of the improved pasture. Disp ersal distance was calculated by measuring the distance, to the nearest mete r, from each owls location outside of the improved pasture to its respective breeding burrow. Two shapefiles, one containing the location of each breeding burrow and one contai ning the locations of each owl outside of the improved pasture, were added to a layer in ArcMap 8.3. The measure tool in ArcMap 8.3 was then used to determin e the dispersal distance.
15 Results Attaching Transmitters Between 4/17/04 and 4/18/04 a total of th ree adult female owls were captured and fitted with necklace transmitters. Behavioral observations over a three day period (4/18/04 4/20/04) showed that the three adult female owls constantly attempted to remove the transmitters. The adult owls ne ver acclimated to wearing necklace radio transmitters and a decision was made to remove the transmitters from adults and only attach transmitters to juvenile burrowing owls. On 4/26/04 two of the adult burrowing owls had stretched the elastic necklace a nd bit through the spli ced cotton string. One transmitter was located approximately 60 meters from the owls main burrow. The other transmitter was located on the burrow mound of the pairs ma in burrow. The third owl was captured using noose carpet traps on 4/30/04 and the transmitter was removed. Table 1 describes the seven juvenile burrowing owls captured and fitted with necklace radio transmitters. Owl number one was captured and fitted with a second radio transmitter due to a transmitter malfunction. Table 1. Juvenile burrowing owls f itted with necklace radio transmitters. Owl Frequency (MHz) Date Attached Sex Weight (G) 1 151.755 (1 st ) 151.690 (2 nd ) 6/6/2004 6/22/2004 Female 131 (1 st ) 111 (2 nd ) 2 151.735 6/6/2004 Unknown 117 3 151.570 6/10/2004 Male 127 4 151.665 6/21/2004 Unknown 129 5 151.530 7/3/2004 Unknown 119 6 151.470 7/12/2004 Unknown 110 7 151.610 7/22/2004 Unknown 139
16 Home Range in Breeding Habitat Hawks possibly killed three juvenile burrowing owls wearing transmitters. The remains of two juvenile owls, a pile of feat hers and the transmitter, were located in the improved pasture on 6/21/04 and 7/22/04. The rema ins of the third juvenile owl, a pile of feathers and the transmitter, were located on 6/20/2004 outside of the improved pasture. The remains were found 366 meters from the owls main burrow in a small clearing within a patch of saw palmetto. One juvenile owl, not wearing a transmitter, was found dead and covered with fire ants ( Solenopsis invicta ) in the entrance of a burrow. The cause of death was unknown. The remaining four juvenile burrowing owls were successfully relocated for 41 out of the 56 days radio telemetry was atte mpted. Radio telemetry ceased for two days due to lightening and for 13 days because two stream crossings were flooded. Table 2 describes the kernel home range estimate for the four remaining juvenile burrowing owls in breeding habitat. A gra phic of the kernel home range estimate for each owl is displayed in the following figures: Fr eq. 151.470 MHz (Figure 4), Freq. 151.530 MHz (Figure 5), Freq. 151.665 MHz (Figure 6), and Freq. 151.690 MHz (Figure 7). Table 2. Kernel home range estimates in breeding habitat. Frequency (MHz) Relocations 95% Kernel Home Range (M 2 ) 75% Kernel Home Range (M 2 ) 50% Kernel Home Range (M 2 ) 151.470 8 176.93 122.57 79.24 151.530 13 185.50 110.10 70.26 151.665 22 104.60 64.44 44.83 151.690 22 97.65 59.86 37.82 Average =141.17 Average = 89.24 Average = 58.04
17 ")")")")!!!!!!!! Figure 4: Kernel home range estimate for frequency 151.470 MHz Legend Improved Pasture!Location of OwlBurrowsType of Burrow") Main")SatelliteKernel Home Range EstimateArea 79.24 Square Meters 122.57 Square Meters 176.93 Square Meters 07014035Meters
18 ")")")")!(!(!(!(!(!(!(!(!(!(!(!(!( Figure 5: Kernel home range estimate for frequency 151.530 MHz 07014035Meters Legend Improved Pasture!(Location of OwlBurrowsType of Burrow")Main")SatelliteKernel Home Range EstimateArea 70.26 Square Meters 110.10 Square Meters 185.50 Square Meters
19 !!!!!!!!!!!!!!!!!!!!!!")") Figure 6: Kernel home range estimate for frequency 151.665 MHz 05010025Meters Legend Improved Pasture!Location of OwlBurrowsType of Burrow")Main")SatelliteKernel Home Range EstimateArea 44.83 Square Meters 64.44 Square Meters 104.60 Square Meters
20 ")")!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!( Figure 7: Kernel home range estimate for frequency 151.690 MHz 0306015Meters Legend Improved Pasture!(Location of OwlBurrowsType of Burrow")Main")SatelliteKernel Home Range EstimateArea 37.82 Square Meters 59.86 Square Meters 97.65 Square Meters
21 From 8/1/02 to 8/2/02 hourly relocati ons were conducted on the four juvenile burrowing owls from 9pm 5am. Table 3 desc ribes the results of the evening telemetry session. Each juvenile burrowing owl was extr emely active in the evening. No signals were located in the pasture after 10 pm. Si gnals, when located outside of the improved pasture, were faint and brief making it difficu lt to triangulate the position of any owl. After midnight, no signals were located in the improved pasture or from the trails surrounding the improved pasture. Table 3. Evening relocations of juvenile burrowing owls. Time Frequency Relocated (MHz) Notes 9 pm 151.665, 151.690 Both located near their main burrow in pasture 10 pm No owls relocated 11 pm 151.665 Located outside of pasture 264 meters from main burrow 12 pm No owls relocated 1 am No owls relocated 2 am No owls relocated 3 am No owls relocated 4 am No owls relocated 5am No owls relocated Flooding of Breeding Habitat Daily rainfall data was collected from a Southwest Florida Water Management District rainfall station, s ite number 528, located approximately 5.8 kilometers from Rutland Ranch. Monthly rainfall data reco rded at site number 528 from 2000-2004, as shown in Figure 8, displays the June to October rainy season in Florida.
The daily rainfall, during July and August, recorded at site number 528 in 2004 is displayed in Figure 9. On 8/6/04 all burrows, except for a main and satellite burrow located in the highest elevated area of the pasture, were flooded. 22 Figure 8: Monthly rainfall amounts for station 528 from 2000-2004 0.002.004.006.008.0010.0012.0014.0016.0018.0020.00Feb-00Jun-00Oct-00Feb-01Jun-01Oct-01Feb-02Jun-02Oct-02Feb-03Jun-03Oct-03Feb-04Jun-04Month and YearRainfall in Inches Figure 9: Daily rainfall at station 528 for July and August of 20040.000.501.001.502.002.503.003.504.004.507/1/047/5/047/9/047/13/047/17/047/21/047/25/047/29/048/2/048/6/048/10/048/14/048/18/048/22/048/26/048/30/04Month and DayRainfall in Inches Figure 9: Daily rainfall at station 528 for July and August of 2004 Figure 8: Monthly rainfall amounts for station 528 from 2000-2004
23Dispersal and Post-Breeding Hom Burrowing owls began dispersing from the improved pasture on 8/6/04. Three out of four juveniles were relocated outside of the pasture on this date. The only juvenile owl relocated in the pasture on this date, frequency 151.665 MHz, was found near one of the non-flooded burrows from which it was born. This juvenile owl finally dispersed from the pasture on 8/17/04. On this date, surface water was found on all areas of the improved pasture. By 9/30/04 all four juvenile owls could not be located within Rutland Ranch nor from the road network surrounding the property. Aerial telemetry was conducted on 10/5/04 to locate the missing owls. The only owl located during aerial telemetry was frequency 151.470 MHz. The pulse rate of the transmitter had slowed from 50 beats per minute to roughly 10 beats per minute. The owl was located 10.83 kilometers southeast of Rutland Ranch. he area where the owl was located is composed of predominantly scrub oak (Gordon 004, personal communication). Dispersal distance for each juvenile owl is shown in able 4. able 4. Dispersal distance of juvenile burrowing owls. Frequency (MHz) Dates Located Relocations Min. Distance from Main Burrow (M) Max. Distance from Main Burrow (M) e Range T 2 T T 151.665 8/17/04 1 366 366 151.470 8/6/04 8/9/04 3 407 10,083 151.690 8/6/04 8/17/04 7 236 337 151.530 8/6/04 9/24/04 15 466 679
24 el displayed in Figure 10. Due to the small number of post-bree ding relocations for each burrowing owl the kernel home range estimate during the post-breeding period was only calculated for the owl wearing frequency 151.530 MHz. The 95% kernel home range estimate equaled 249.17 m 2 the 75% kernel home range estimate equaled 192.230 m 2 and the 50% kern home range estimate equaled 124.83 m 2 A graphic of the kernel home range estimate for this owl is
25 !(!(!(!(!(!(!(!(!(!(!(!(!(!(!( Figure 10: Kernel home range estimate for frequency 151.530 Legend Improved Pasture!(Location of Owl Long Leaf Pine StandKernel Home Range EstimateArea 124.833 Square Meters 192.230 Square Meters 249.167 Square Meters
26 Discussion The early observations of burrowing ow ls in breeding habi tat during the late 1800s indicate that small nomadic coloni es may have been common. Post-breeding dispersal may have allowed burrowing owls to colonize breeding habitat created each year by fire and flooding. These small coloni es may have persisted due to immigration and emigration. A previous population viability analysis indicating high probabilities of extirpation for small populations was modele d after the available data collected on burrowing owls from Cape Coral, Florida (Bowen 2000). This population viability analysis did not include immigration and emigration (Bowen 2004, personal communication), thus possibly el evating extinction rates. The improved pasture at Rutland Ranch is burned yearly in January to create suitable breeding habitat for burrowing owls (VanGelder 2003, pe rsonal communication). Ten pairs of adult burrowing owls were located within the improved pasture in 2001 (Barnwell et al. 2003) and in the spring and summer of 2003 ten pairs of adult burrowing owls were located at Rutland Ranch (persona l observation). In 2004, five pairs of adult burrowing owls were located in the pasture a nd only three of these pairs fledged young. It is unknown if the smaller adult population in 2004 is due to low immigration, high predation, or low territory fidelity. The location of burrows in the pasture as shown in Figure 2 suggests that adult owls may have selectively excav ated burrows in the higher elev ated areas of the pasture. During the first survey for burrows on 3/26/04 the areas of lowest elevation within the pasture did not contain surface water. Thes e findings concur with Hoxie (1889), Scott (1892) and Palmer (1896) who located burrows in the highest elevated areas of pasture. Unfortunately, neither water table data nor po tentiometric surface maps for the Floridan Aquifer, Intermediate Aquifer, and Tamiam i Upper Hawthorne Aquifer were available for the improved pasture during the first su rvey in March of 2004. A high water table, evenly distributed under the improved pasture, could further support the hypothesis that burrowing owls were selectively excavating bu rrows in the higher areas of the improved pastures. Alternatively, the distribution of burrows during the 2004 breeding season may
27 colonial nature of burrowing owls. More resear ch needs to be conducted to ter f of the main these sighting, 7/29/04, a ons, s r a nother pair of adult burrowing owls was omple o g and American alligator ( Alligator mississippiensis). be due to the understand the distribution of burro ws in rural breeding habitat. Vegetation, especially dog fennel ( Eupatorium capillifolium ), grew quickly af the January burn in 2003. By the time the majo rity of burrows had been excavated in March of 2004, large patches of dog fennel surro unded the main and satellite burrows o two pairs of adult burrowi ng owls. Both of these pairs successfully fledged young. The areas of thick vegetation may ma ke the burrowing owls susceptible to predation by hawks. On two occasions, an unidentified hawk was flushed from the ground within a large patch of dog fennel that grew roughly within 50 meters burrows for two burrowing owl pairs. Duri ng the second of hawk flew up from within the patch of dog fenne l, caught an owl in the air with its tal and both owl and hawk tumbled to the ground. The owl escaped and survived the encounter with the hawk. On 5/21/04 an adult and juvenile red-tailed hawk ( Buteo jamaicensis) were seen hunting along the fence line surrounding the improved pasture. Other unknown predators also preyed upon burrowing owls in the improved pasture. On 4/18/2004, the main burrow for one pair of adult burrowing owls was completely excavated. There was no sign of the adults and no burrowing owl remain were located. The satellite burrow fo ctely excavated on 6/2/04. The banded adult female and the male were located tw weeks later at a new burrow approximately 100 meters from their previously excavated burrow. In an attempt to document potential pr edators of burrowing owls during breedin season, a CamTrakker infrared camera was setup approximately 25 meters from the main burrow of one burrowing owl pair. After three days of monitoring, the only animal documented by the infrared camera was a raccoon ( Procyon lotor ). Other wildlife seen in the pasture include whitetail deer ( Odocoileus virginianus ), feral hogs ( Sus scrofa ), armadillo ( Dasypus novemcinctus ), coachwip snake (Masticophis flagellum ), eastern diamondback rattlesnake ( Crotalus adamanteus ), and black racer (Coluber constrictor ). Wildlife seen outside of the pasture includes coyote ( Canis latrans), bobcat ( Lynx rufus ),
28 riod. After the young s ested ed ) nge hich to e difficulty in locating burrowing owls in breeding habitat during the evening lemet ide the n, ture for 3-11 days before dispersing In the daytime relocated juvenile burrowing owls were consistently located within the vicinity of the main or satellite bu rrow during the breeding pe are able to fly they are dependent upon the main or satellite burrows for up to 60 days (Mealey 1997). The home range estimates of juvenile burrowing owls in the breeding habitat indicates that the juvenile owls were extremely dependent on the main and satellite burrows. The null hypothesis that post-breeding home range for adult burrowing owl would not be significantly diffe rent in size from breeding home range could not be t in this study. Adult burrowing owls neve r acclimated to wearing necklace radio transmitters. In a personal communication afte r completion of my fieldwork it was not that adult Western burrowing owls also never acclimated to wearing necklace radio transmitters (Gervais 2004). After two to three days juvenile burrowing owls acclimated to wearing the necklace radio transmitters. The home range estimates for juvenile burrowing owls may be overestimated due to the small number of relocations per owl. Seaman et al. (1999 recommend that a minimum of 30 locations ar e required to get an accurate home ra estimate using the kernel method. The inacce ssibility of the improved pasture due to stream flooding during the rainy season reduced the number of opportunities in w relocate juvenile owls. In hindsight, more than one relocation pe r day for each burrowing owl would have increased the sample size. Th tery session suggests that the juvenile ow ls avoided the improve d pasture at night. During the evening, there were several brief and faint relocations of j uvenile owls outs of the pasture, but a locat ion could only be estimated for one juvenile owl. Dispersal from breeding habitat coinci ded with the flooding of the pasture and burrows beginning on 8/6/04. Once an owl disper sed it was never again relocated in improved pasture, even after the pasture had dried due to evapotra nspiration, infiltratio and surface runoff. During the daytime juvenile burrowing owls utilized dissimilar habitat from the improved pasture. Three out of four juvenile owls were found utilizing the extensive saw palmetto patch surrounding th e pas
29 ) ls he range of the receiver. A de crease in pulse rate would infer that the transmi bitat. rial telemetry a ssisted in locating onl y one out of four juvenil other the veniles r beyond the range of the receiver. One of these ju venile owls also utilized several live oak trees growing near the improved pasture. A Florida scrub jay ( Aphelocoma coerulescens also utilized these live oak tr ees. The fourth juven ile owl spent 18 days in the extensive saw palmetto patch before dispersing be yond the range of the receiver. There was no noticeable change in pulse rate (beats per minute) for any transmitters before the ow dispersed beyond t tter battery would soon fail. The different habitat preference for juvenile burrowing owls during the breeding and postbreeding period refutes the null hypothesis that breeding habitat would not be comparativ ely different from post-breeding ha The large areas of private land surr ounding Rutland Ranch coupled with the limited access to these properties made it difficult to locate burrowing owls from the surrounding road network. Ae e burrowing owls. This may have been due to possible battery failure for the three radio transmitters. The burrowing owl su ccessfully located was the last bird on which a transmitter was attached. The drastic reduction in beats per minute for this transmitter indicated that th e battery would soon fail. The use of feathers for DNA PCR analysis was not successful in determining sex of juvenile burrowing owls. This may ha ve due to an inadequate amount of tissue within the calamus, the portion of the feather in the skin after the feather was pulled from the chest area. The wearing of radio transmitters may have had an effect on burrowing owls in this study. Only one owl wearing a transm itter was recaptured and weighed a second time. This owl lost 20 grams in sixteen days More research is needed in order to determine if weight loss was due to the eff ect of wearing a transmitter, the ju beginning to forage on their own, less food being given to juveniles from adults, or othe unknown factors. This research was the first documentation of burrowing owl ecology in a rural environment. The small sample size in this study only provides a partial clue to the ecology of burrowing owls in rural areas. Th ere is still much to learn about this subspecies, especially habitat requirements after burrowing owls have dispersed from
30 t 3). e of orida. breeding habitat. For example, it is not known if burrowing owls utilize specific habitats or a variety of habitats during dispersal a nd the post-breeding period. Determining habitat requirements is particularly important because of the past and current loss of habitat in Florida due to development and agriculture. Floridas popu lation is the third fastest growing in the nation (U.S. Census Bureau 2004) and a variety of hab itats are being los such as upland forests (Sprott and Mazzotti 2001), scrub oak (Myers 1990), and prairie habitat (Abrahamson and Hartnett 1990). The burrowing owl has been listed as a Species of Special Concern since 1979 by the Florida Fish and Wildlife Conservation Commission (Millsap 1997) and also as a Bird of Conservation Concern by the U.S. Fish and Wildlife Service (Klute et al. 200 Without conservation and management it may be listed as a threatened species becaus vulnerability to habitat modification, envir onmental alteration, human disturbance, or human exploitation (Florida Fish and Wildlife Conservation Commission 2004). A greater understanding of burrowing owl ecology in rural environments is required in order to determine management and conservation strategies for this subspecies in Fl
31 ls nd f a ood factors (McGowan 2001). Theref ore, research from a variety of disciplines, geographic areas, and temporal scales may be require d in order to understa nd the ecology of a species (Marzluff and Salabanks 1998). Previous detailed studies have documente d the prey preference of burrowing owls such as Lewiss (1973) analysis of tabulat ed records of stomach contents from 19071929, Hennemanns (1980) research at an industrial park, and Wesemanns (1986) analysis in an urban area. These studies ha ve shown that the most frequent prey of burrowing owls is insects (Lewis 1973, Wesemann 1986). Documentation of prey preference for burrowing owls in rural areas has been mostly observational (Ridgeway 1874, Cahoon 1885, Hoxie 1889, Rhoades 1892, Palm er 1896, Bent 1938, Sprunt 1954), but also suggests that insects are a major prey item. Prey of burrowing owls, other than ins ects, found in urban and industrial areas includes crayfish (Procambarus alleni ), least tern (Sterna antillarum ), cotton rats ( Sigmodon hispidus ), rosy wolf snail (Euglandia rosea ), marsh crab ( Sesarma reticulatum ), Cuban tree frog (Osteopilus septentrionalis ), southern toad ( Bufo terrestris ), Comparison of Diet and Potential Prey for Rural and Urban Burrowing Ow During the Breeding Period Introduction Management and conservation of a speci es requires understandi ng its habitat a food requirements, which can vary over sp ace and time (Litvaiti s et al. 1996). For example demographic information, prey preference, and habitat requirements of a species collected from research on a small spatial sc ale may not extrapolate to a larger spatial scale (DeSante and Rosenberg 1998). Further, a shift in the geogra phic distribution o species over time, such as from historically rural to urban areas, can affect a species f use, size of territory, exposure to predators, social structure, and basic demographic
32 eastern spadefoot toad (Scaphiopus holbrook ammals from the Genus Peromyscus and Sylvilagus (Owre 1978, Hennemann 1980, Wesemann 1986). Prey remains other than insects found in rura l environments include savannah sparrow ( Pa f rodents, crayfish, snakes, frog Bent 1938, Nicholson 954). methods have been used to document the diet of burrowing owls in sis of stomach contents (Palmer 1896, Bent 1938, Lewis 1973), lson rial n a prey t, and i ), and m sserculus sandwichensis ), bobolink ( Dolichonyx oryzivorus ), and unknown species o s, and minnows (Rhoads 1892, 1 Various Florida including: analy regurgitated pellets (Hox ie 1889, Palmer 1896, Neill 1954, Hennemann 1980, Wesemann 1986), and uneaten prey remains found near burrows (Bent 1938, Neill 1954, Nicho 1954, Owre 1978, Hennemann 1980, Wesemann 1986). Each method on its own may not accurat ely represent the prey preference of burrowing owls. Prey remains found in regur gitated owl pellets have been used to identify individual prey (Errington 1930, Neill 1954, Hennemann 1980, Wesemann 1986). This method may not accurately represent an owls diet because skeletal mate of large prey may not be consumed (Thomp son 1971). Other methods such as visual observation of predation (Grant 1965), should be used to gain further information o species diet. The purpose of this study was to compare the diet and potentia l prey of burrowing owls in a rural environment and an urban e nvironment. Due to lack of information on post-breeding habitat requirements of burro wing owls in Florida, the study area was limited solely to breeding habitat. In both ru ral and urban environments, I compared remains found in regurgitated pellets, richness of small mammals in breeding habita richness of insects in breeding habitat.
33 3 to ion of 15,000 residents and the winter population peaks at roughly 35,000 people ousing lots. In 2005 burrowing ere nal llammal trap was placed every ten meters along each of the five transects fty me r The five transects at Rutland Ranch were 50 meters in length and randomly laced in the rectangular improved pasture co ntaining burrowing owls as shown in Figure 1. The placement of each transect was dete rmined by the following procedure: One orner of the rectangular past ure, the southeast corner, was designated the origin. The two erpendicular sides of the rectangle emanating from the origin were designated X and Y. he X and Y sides were measured to the nearest meter and the starting point for each Methods The study occurred on Marco Island a nd Rutland Ranch from October 200 October 2004. Marco Island is a large barrier island, 36.25 square kilometers in size, located off the southwest coast of Florida as shown in Figure 1. It has a permanent populat (Marco Island City Hall 2003). On Marco Island the vast majority of burrowing owls are found breeding on vacant housing lots. In 2004 there were approximately 1,080 vacant housing lots and 113 of these lots were occupied by a total of 171 adult burrowing owls. Only three pairs of owls were found breeding on property other than vacant h owls occupied 83 vacant housing lots. Based on the rate of new home construction th will be no vacant housing lots on Marco Is land by 2011 (Nancy Ritchie 2005, perso communication). Sherman small mammal traps were utili zed to compare the richness of small mammal species on Rutland Ranch and Marco Island. Five species of small rodents found in Florida may be potential prey of burrowing owls (Schmidly et al. 1999). One Sherman sma m fiters long. The baits for traps consisted of either a ro lled oats/shelled peanuts or shelled peanuts (Patric 1970) An insecticide was sprayed on the ground in a two-mete circumference around each trap to deter loss of bait due to ants (M itchell et al. 1996). Small mammal trapping was conducted every other month for a two-day period in both research areas. Traps were set at sunset and checked each morning. Each small mammal trapping session consisted of 50 trap nights: 25 traps x 2 trapping nights. p 1 c p T
34 ent was the southeast corner. The starting point for each transect was etermined by using a random number table to generate two distances in meters, X and oved measurem d Y, from the southeast corner. Figure11: Location of transects, pitfall traps, and small mammal traps within impr pasture at Rutland Ranch The random number generated for the X distance represented the starting points distance north of the southeas t origin. The random number generated for the Y distance represented the starting points distance west of the south east origin. A random number table was then used to select a number from 1-360, which determined the compass bearing for the direction of each transects endpoint. Y-coordinate X-coordinate732 meters Origin930 meters Legend Burrow Transect Insect Pitfall Trap Small Mammal Trap Y-coordinate X-coordinate732 meters Origin930 meters Legend Burrow Transect Insect Pitfall Trap Small Mammal Trap
35table was used to determine which lots would contain ansects. Vacant lots on Marco Island are 80 X 100 feet or 80 X 110 feet in size (Nancy Rdicular transects forming the shape of the letter T. One aper envelope labeled with the date and location. A dissecting microscope was used to entify insects based on the remains of body parts found in pellets. The mandibles, ones e assistance of the Florida Museum of Natural History (Candace McCaffery 2004, personal communication). One transect was placed on one of five vacant lots on Marco Island containing burrowing owls. Every vacant lot containing burrowing owls was assigned a random number and a random number tr itchie 2005, personal communication). Due to small lot size, each fifty meter transect as divided into two perpen w transect was thirty meters in length and the other twenty meters. Insect pitfall traps were placed in both research areas to compare the richness of insect species over time (Wesemann 1986). Two pitfall traps were placed 5 meters away from the starting point of each transect. A random number table was used to select the compass bearing for the direction of each pitfall trap. The pitfall traps were made of #10 size cans buried in the ground and level with the soil surface (Wesemann 1986). A few inches of water was placed in the bottom of the cans to stop insects from climbing out (Wesemann 1986). Pitfall traps were baited with either spoiled meat or fruit (Wesemann 1986). A covering made of Plexiglas and wire mesh was placed a few inches above each trap to deter rain and predators. Insect trapping was conducted every other month for a two-day period. Traps were checked each morning and captured insects were removed. Each insect trapping session consisted of 20 trap nights: 10 traps x 2 trapping nights. Insects were identified to the Family level. Regurgitated pellets were collected every other month in both the rural and urban breeding habitat. I searched for pellets within a radius of several meters of five randomly selected burrows on both Marco Island and Rutland Ranch. Each pellet was stored in a p id heads, elytra, legs, and forceps were examined to identify and count insects and arthropods to the level Family in each pellet (Gleason and Craig 1979, Wesemann 1986). Researchers from the Florida State Collection of Arthropods assisted in classifying insect and arachnid remains within pellets (Paul Skelley 2004, personal communication). Band or bone fragments in pellets were classified with th
36 Results rap insects caught were from th No small mammals were captured in the small mammal traps during the 300 t nights at either research area. Insect pitfall tr aps were set in both research areas for a total of 120 trap nights. The prey captured in the Marco Island p itfall traps consisted of five orders of insects and one order of spiders (Table 5). The largest numbers of e family Gryllidae. Eighteen organisms were captured in the insect pitfall traps. The prey captured in the Rutland Ranch pitfall traps consisted of four families of insects and one family of spiders (Table 6) The largest numbers of insects caught were from the family Gryllidae. Sixty-six organisms were captured in the insect pitfall traps. Table 5. Organisms captured in p itfall traps at Marco Island. Class Order Family Quantity Insecta Orthoptera Gryllidae 6 Insecta Coleoptera Carabidae 5 Insecta Diptera 4 Insecta Hemiptera Cicadellidae 1 Insecta Hemiptera Gelastocoridae 1 A rachnida Araneae Clubionidae 1 Table 6. Organisms captured in pitfall traps at Rutland Ranch. Class Order Family Quantity Insecta Orthoptera Gryllidae 29 Arachnida Araneae Clubionidae 24 Insecta Coleoptera Carabidae 7 Insecta Orthoptera Acrididae 4 Insecta Orthoptera Tettigoniidae 2
37 he analysis of the 55 pelle ts collected on Marco Island is displayed in Table 7 hile Table 8 displays the an alysis of 31 pellets collected at Rutland Ranch. A graph of the perc ey remains in pellets from Marco Island and Rutland Ranch T w entage of prey found w ithin all the pellets, organi zed by class for each research area, is shown in Figure 12. Figure 12: Pr Prey ts from Rutland8.2 1.74 0.210 20 60 8 100 Insecta ArachnidaGastropoda Aves Mammalia ClassPercentage remains in pelle Ranch 89.12 8 0.65 40 0 Prey Prey remains in pellets from Marco Island85.92100 2.88 0.96 0.32 9.120 20 4 8 Arachnida ReptiliaGastpodaMammalia ClassPercen 0.80 0 60 0tage Insecta Aves ro Prey Prey remains in pellets from Marco Island Prey ellets from remains in p Rutland Ranch
38Table 7 Marco Island: Analysis of pellets and remains found on burrows. Prey Remains in Pellets Class Order Family Total Percentage Insecta 00 196 31.36 Insecta Dermaptera 58 9.28 Insecta Orthoptera Acrididae 23 3.68 Insecta Coleoptera Carabidae 5 0.80 Insecta Coleoptera Curculionidae 5 0.80 Arachnida Araneae Clubionidae 57 9.12 Aves 18 2.88 Reptilia Squamata Polychrotidae 6 0.96 0.80 Coleoptera Scarabaeidae 250 40. Insecta Orth optera Gryllidae Gastropoda Stylommatophora Spiraxidae 5 Mammalia Rodentia Muridae 2_ 0.32 625 100 Prey Remains Found on Burrow Mound Class Order Family Total Aves 2 Mammalia Rodentia Muridae 2 Reptilia Squamata 1 Amphibia Anura Hylidae 1
39 Table 8. Rutland Ranch: Analysis of pellets and remains found on burrows Prey Remains in Pellets Class Order Family Total Percentage Insecta Coleoptera Scarabaeidae 146 31.81 Insecta Dermaptera 127 27.67 crididae secta Hemiptera Reduviidae 7 1.53 a e nida raneae lubionidae da Insecta Orthoptera A 48 10.46 Insecta Orthoptera Gryllidae 47 10.24 Insecta Coleoptera Carabidae 19 4.14 Insecta Coleoptera Curculionidae 11 2.40 In Insecta Coleopter Cerambycida 4 0.87 Arach A C 38 8.28 GastropoStylommatophora Spiraxidae 8 1.74 Aves 3 0.65 Mammalia Rodentia 1 0.21 100 459 Prey Remains Found on Burrow Mound Class Order Family Total oleoptera ter eptilia Squamata Polychrotidae 1 InsectaC Scarabaeidae 4 Insecta Orthoptera Acrididae 3 Insecta Coleoptera Carabidae 1 Insecta Lepidopa 1 R
40 t Marco I veryects. The e short tra 2 nightsv ery other month),umber f some insect species (Arnett 2000), and or possibly low ts. A far numbers due field time ad Ranc greater nsts were fall traputland R sland, but ng did not reption of tial rey of burrowing owls. For example, no insects from the family Scarabaeidae were e the mquent pr in egurgitated pellets. Pitfall tr aps have previously proven su ccessful in capturing insects ily (G ). T resentatipr ey itemd in itfall traps may be due to bu rrowing owls feeding outside of the improved pasture in the g. A greaterariety of incts may have been captured all traps h laced in any of the habitats surrounding the improved pasture. Small Mammal Traps sons why no small mammals were caught in longer tr als ethe bait d, th e bait of shelled peanuts and d peanuts a combinhave beenfective. Peanut butter, rapping dman et al. 1996), ore arom ts and us a better attractant. Third, small mammals r improved pasture. Discussion Insect Pitfall Traps The insecpitfall traps onsland captured few insis may b due to thpping period ( e small nof insect pitfall traps, the short life cycle o number of insects species found within the va cant logreater of insect were seen on breeding habitat at Rutland Ranc h than at Marco Island, but this may be to more spent at Rutlnh. Aumber of inec caught in pits on Ranch than Marco Ipitfall trappi give an accurateresentahe potent p caught in pitfall traps, but insects from this family werost freey found r from this famoehring et al. 2002he poor repon of s capture p evenin vse if p itfad been p There are a number of possible rea the small mammal traps. First, a apping period might have given small mamm a greater opportunity to disc ovr ed traps. Secon or shelle and rolled o tsation may inef used in previous small mammal t studies (Patric 1970, W oo may be matic than peanut h may not be commonly located on either th e vacant lots o
41 nd n of prey remains found on burrow mounds further elucidated the iet of burrowing owls on Marco Island. Prey remains included Cuban Tree Frog Osteo ms s e Cape Coral study 70 ellets were collected in December of 2004 and May of 1985 (Wesemann 1986) versus Marco Isla nd from October 2003 October 2004. The pellet analysis results from Rutland Ra nch indicate that insects were the most e On 5/6/04, Burrow Mou The collectio d ( pilus septentrionalis ), Cotton Rat ( Sigmodon hispidus ), bird bones, and the remains of a snake, rodent, and frog, which were too decomposed to classify. The prey remains found on burrows mounds at Rutland Ranch consisted of insects and in one instance the bones of an Anole. Pellet Analysis The analysis of pellets from Marco Isla nd indicates that insects were the most frequent prey item. Interestingly, arachnids a nd birds were two other frequent prey ite of burrowing owls. Hennemann (1980) and We semann (1986) reported finding birds as prey, but not as frequently as in this study. Only six pellets on Marco Island contai ned the remains of Anolis (genus). Previous pellet analysis on Cape Coral, Fl orida found a higher percentage of Anolis remains within pellets (Wesemann 1986). The differing results between the two studie may be due to different sample sizes and sampling periods. In th p 55 pellets collected on frequent prey item. Another frequent prey item were ar achnids, which were commonly seen in the pasture (personal observation). One insect family, Cerambycidae, provides a clue to the foraging patterns of burrowing owls in rural environments. Insects from this family are woodborers and are not commonly located in pa stures (Paul Skelley 2004, personal communication). At Rutland Ranch adult male and female burrowing owls were seen hunting in th improved pasture in the daytime. The most fr equent prey items were insects.
42 rrowing owl brought a rodent (species not known) to an adult female. urrowing owls were never seen preying on birds although several bird species were in ts sects from one Order and seven Families while the rco Island contained insects from one Order and five Families. Burrowing eous urban environments may be supplementing their diet with anoles esemann 1986) or birds because of the re duced availability of insects. d ont ains pine flatwoods, oak scrub, riparian t of d sed to determin e factors which may limit burrowing owl an adult male bu B commonly seen in the pastur e such as Mourning Dove ( Zenaida macroura) and Eastern Meadowlark ( Sturnella magna ). Although there was not a large difference in the percentage of insects found pellets at both research areas, 85 % on Marc o Island versus 89 % at Rutland Ranch, a greater variety of insects wa s discovered in the pellets fr om Rutland Ranch. The pelle from Rutland Ranch contained in pellets from Ma owls in homogen (W These results suggest that a heteroge neous rural environment may present a greater opportunity for burrowing owls to feed on insect prey than a homogeneous urban environment. The improved pasture at Rutland Ranch is composed of various grasses an herbaceous vegetation. Rutland Ranch also c hardwoods, and herbaceous marshes (Barnwell et al. 2003). The ur ban environmen Marco Island is composed of either vacant housing lots that are routinely mowed, developed lots containing office buildings or ho mes, and open areas such as small parks, athletic fields, and playgrounds. Developed lo ts and open areas are commonly compose of monoculture lawns and sm all areas of trees and or shrubs, which are commonly sprayed with insecticides to control insects. Due to the small number of pellets collected (55 pellets from Marco Island versus 31 pellets from Rutland Ranch) a note of cau tion should be taken when comparing the results of pellet analysis. A larger sample size from both research areas may provide a different interpretation when comparing the diet of burrowi ng owls from rural and urban areas. Research has been u populations in urban areas. Some of these limiting factors include loss of nest burrows and nesting habitat to co nstruction, human harassment of burrowing owls, nest
43 l ence, a nd habitat requirements (breeding and postuld ld allow abandonment due to extensive vegetative gr owth around burrows, and predation by fera and domestic cats and dogs (Millsap and Bear 1988). The majority of information on burrowing owls in rural areas is observationa l. There are no detailed studies documenting productivity, survival, prey prefer breeding) of burrowing owls in rural areas. It s not known if factors other than habitat loss contributed to the declin e of burrowing owls on the dry prairies of south central Florida. Proactive research, research which de termines factors limiting populations, co be an important tool in the conservation of burrowing owls throughout the state. This may require research from a variety of di sciplines over various spatial and temporal scales (Marzluff and Sallabanks 1998). The re sults of proactive re search cou focused conservation efforts instead of possibly expensive future burrowing owl restoration projects.
44 tion 0). Current conservation and management strategies for burrowing owls in Florida focus on urban/suburban populations (Millsap and Bear 1988, Haug et al. 1993, Mealey 1997, Bowen 2000, Millsap and B ear 2000), because the majority of previous research on this subspecies has been conducted on suburban and urban populations in south Florida; specifically Lee, Dade, and Broward counties (Wesemann 1986, Millsap and Bear 1988, Mealey 1997, Mi llsap and Bear 1997, Millsap and Bear 2000). The change in the geographic distribution of a species over time, from a rural to urban environment, can affect basic demographic factors, food use, size of territory, exposure to predators, and social structur e (McGowan 2001). Therefore, management and conservation strategies designed for burro wing owls in urban environments may not be suitable for burrowing owls in rural environments. Behavioral observations of burrowing owls in rural environments can be one tool to predict the consequences of future management and conservatio n strategies in rural areas. Behavioral Observations of Adult a nd Juvenile Burrowing Owls during the Breeding Period Introduc Wildlife management and conservation plans are often design ed to reduce the effects of anthropogenic disturbances to animal populations and their habitats. By understanding the interaction between an animals ecology and behavior, we can help predict the consequences of specific wildlife management or conservation actions (Macdonald et al. 200
45 Some forms of behavior that have important implications for wildlife management and conservation include juvenile dispersal, habitat selection, courtship behavior, daily and seasonal activities, territorial defense, flocking, renesting, migration, and s from the early nineteenth cen tury to present have descri bed the behavior of this bspecies. Bowen (2000) was the first to quantify specific behaviors of adult and ing owls during a demographi c, distribution, and me tapopulation analysis f the species throughout Florida. The be haviors recorded include roosting, hunting, ry response to predators (Bolen and Robi nson 1999). Observations of burrowing owl su juvenile burrow o feather maintenance, practicing flying, burro w maintenance, feeding young, and territo defense (Bowen 2000). The purpose of this study was to documen t the behavior of adult and juvenile burrowing owls in rural habitats, specif ically during the breeding period. This information could aid in predic ting the effect of management and conservation strategies for burrowing owls in rural environments.
46 urred n for adu lt burrowing owls (Table 9) and juvenile burrowing owls 00). behaviors. Behavior Definition Methods We observed burrowing owls located at Rutland Ranch as shown in Figure 1. Behavioral observations were conducted from 5/4/04 6/2/04 in the improved pasture on all ten adult burrowing owls and nine juveni le burrowing owls. Observations occ between 10am and 8pm. Radio transmitters we re not attached during the observatio periods because trapping, handling, and atta ching transmitters can alter an animals behavior (White and Garrott 1990). I created an ethogram that describe d the behaviors that were observed (MacDonald et al. 2000) (Table 10). The choice of which behavi ors to document was based on personal observations and previous documentation of burrowing owl activity (Bowen 20 Table 9. Ethogram of adult burrowing owl Preening Cleaning feathers with beak Scanning Quickly glancing at surrounding ground or sky Hunting Jumping on prey from gr ound or diving at prey from air Dozing Closing eyes for five or more seconds while perching Vocalizing Making calls or sounds Digging Owl in burrow and sand er upting from burrow entrance Feeding Self Eating prey captu red by self or another adult Thermoregulation Sitting or perching with wings extended and/or performing gular flutter. Feeding Young Female taking food from male and feeding young
47 thogram of juvenile burrowing owl behaviors. Behavior Definition Table 10. E Scann ing Quickly glancing at surrounding ground or sky Dozing Closing eyes for five or more seconds while on burrow mound Being fed by Adult Receiving food captured by adult male or female Vocalizing Making calls or sounds Digging Owl in burrow and sand er upting from burrow entrance Practice Flying Flapping wi ngs and jumping up from ground Stretc ht. h Wings Quickly opening wings from body. No attempt at flig Running into Burrow Owl running into burrow The behavior of one pair of adult burrowing owls and/or young was documented mpli ng at five minute intervals (Altmann 1974, MacDonald et al. 2000). Two pairs of adult burrowing owls and/or young were simultaneo rchers were present. Behavioral obwhich ran serving owls through a spotting scop ervation period an attempt was m nd record theserved a gned each or absence of young: male s without young, females raising young. bined to i or each category. y ob oved pasture as recorded (Table 11). Each instantaneous scan was considered a point event and the ansition probabilities, the probability of an adult burrowing owl going from one location the improved pasture to another locati on, was calculated for each category of adult during each observation period by instantaneous scan sa usly observed when two resea servations, ged from one to f our hours, were recorded by ob e from a distance of roughly 100 meters. During each obs ade to locate each adult burrowing owl and/or young a behavior ob t five minute intervals. I assi adult owl to one of four categories based on the presence s without young, males raising young, female The results for all adult owls within each category were com ors observed f document the behav During ever servation the location of each adult owl in the impr w tr in
48 Table 11. Description of adult burrowing owl locations at Rutland Ranch. on of owl Locati Definition Burrow Owl on burrow mound, in burrow entrance, or inside burrow Not at Burrow Owl located anywhere in pasture except at burrow Missing Location of owl unknow n baccouprobability of awing ow) was co P b/m = urrowing owls (H and Meelis 1992). For example, the transition dult male burro ls without young going from the burrow (B) to missing (M alculated using the foll wing formula: mN N mbN, re all aisin young is independent of sex. HO: g young is independent of sex. O: Th b,m equals the total number of times all burrowing owls in this category wedocumented as going from the burrow to missing. N m equals the total number of timesburrowing owls in this category were documented as missing. The G-test of independence for 2 X 3 contingency tables was used to test two hypotheses regarding the location of adult burrowing owls in the improved pasture (Table11). H O : The location of adult burrowing owls rg The location of adult burrowing owls not raising young is independent of sex. The G-test of independence for 2 X 8 and 2 X 9 contingency tables was used totest two hypotheses regarding the behavior of adult burrowing owls in the improved pasture. H O : The behavior of adult burrowing owls raisin He behavior of adult burrowing owls not raising young is independent of sex.
49 esults Adul tely 31 r at Rutland Ranch. A graph of female re 14) burrowing owls with young dicates the behaviors observ ed during the breeding period. R ts with Young Approxima hours were spent obser ving burrowing owl behavio (Figure 13) and male (Figu in Figure 13: Behavior of adult female burrowing owls raising young30 0 10 105911 115912 125913 135914 145915 155916 165917 175918 185919 195920 2059Time 5 10Num 15 25ber of Occues 20rrenc preening scanning hunting feeding young vocalizing digging feeding self thermoregulation Figure 14: Behavior of adult male burrowing owls raising young20 0 5 1 10 105911 115912 125913 135914 145915 155916 165917 175918 185919 195920 2059TimeNumb 10 5er of Occurrences preening scanning hunting dozing vocalizing thermoregulation Figure 13: Behavior of adult fema le burrowing owls raising young Figure 14: Behavior of adult ma le burrowing owls raising young
canning was the most frequently observed behavior for both male and female wls with young during any observation period. Thermoregulation and hunting were the st frequent behaviors for both sexes. Both male and female adult urrowing owls raising young were observed hunting during the daytime on six the four categories (males rowing ols raising young within the improved pasture were different. The results of the G-test of independence do not support the null hypothesis of no association between sex and location G = 35.157 > 2 (0.05, 2) = 5.991. Table 12: Sum of locations for adult owls during five minute observation periods Young Present Yes/No SexMain Burrow Satellite Burrow Sum Sightings at Burrows Not at BurrowMissing Total Numbr Observations S o second and third mo b occasions. The results of the G-test of independence support the null hypothesis of no association between sex and behavior G = 10.721 < X 2 (0.05,8) = 15.507. The locations of adult burrowing owls within each of without young, males raising young, females without young, females raising young) were combined an d displayed in Table 12. The locations of male and female bur w e Yes F 80 26 106 50 24 180 Yes M 65 9 74 33 73 180 No F 52 3 55 32 68 155 No M 45 12 57 36 62 155 The transition probabilities, the probability of an owl going from one location in the improved pasture to another are shown in Table 13. The most frequent transition for males was from the burrow to somewhere within the improved pasture (0.66). This was very similar to the probability of a male transitioning from somewhere within the pasture to missing (0.62). The lowest transition probability calculated was an adult male moving from the burrow to missing (0.33). 50
Table 13. Tnobilities for adult burrowing owls ris n T o Not at Burrow Missing 0.80 0.20 rasitin pr oba ais ng y oung versus adults not rai ingyoug Males without Young Fe males hout Young wit To Not at Burrow Missing 0.44 0.56 To Bu Burrow 0 rrow t at Burrow .00 0.54 0.46 No M issi ng Burrow Burrow0.00 From Not at Burrow 0 .63 0.00 0.3Fr 7 om Nt ot a Burrow0.62 0.00 0.38 Missing 0 .712 0. 9 0.00 Missing0.80 0.20 0.00 Males with Young T o Female s ung with Yo rrowNot at rowMi .000.33 Bu Burrow 0 Burrow Burrow0.00 Bur iss0.66 ng From Not at Burrow 0 .38 0.00 0.62 Fr om Not at0.0 0 0.15 Burrow0.85 Missing 0 .50 0.50 0.14 0.00 Missing0.86 0.00 51
The most frequent transition for females was from missing to a female located at the burrow (0.86). This transition was very similar to the probability of an adult female going from somewhereasture to the burrow (0.85). The lowest transition alculated wassing to a female located some the ture (0.14). Thisry similar to the probability of an aale transitioning somewh to missing (0.15). The graph of femamale (Figure 16) burrowing owls without ng the breeding period. Scanning was the dult male and female owls. second most ulat dmented nine times emales and eight times fales. The third most frequently observehavior for es). Preening was the third mes). The resultpendence do not sll hypothesis of no association and avior G = 20.619 >.067. Figure 17 indicates theeriods for dult burrowing the improved pasture. The most frequent transition for females was from missing to a female located at the burrow (0.86). This transition was very similar to the probability of an adult female going from somewhereasture to the burrow (0.85). The lowest transition alculated wassing to a female located some the ture (0.14). Thisry similar to the probability of an aale transitioning somewh to missing (0.15). The graph of femamale (Figure 16) burrowing owls without ng the breeding period. Scanning was the dult male and female owls. second most ulat dmented nine times emales and eight times fales. The third most frequently observehavior for es). Preening was the third mes). The resultpendence do not sll hypothesis of no association and avior G = 20.619 >.067. Figure 17 indicates theeriods for dult burrowing the improved pasture. 52 2 ws ws ithifrithifr n tomn tom he p mihe p mi probability cpasfrom Adults without Young young indicates the behaviors observed durimost frequently observed behavior of both afrequently observed behavior was thermfor fmale burrowing owls was hunting (four timobserved behavior for femindebehall aprobability cpasfrom Adults without Young young indicates the behaviors observed durimost frequently observed behavior of both afrequently observed behavior was thermfor fmale burrowing owls was hunting (four timobserved behavior for femindebehall a whewhe rere wi wi thinthin was veithin the was veithin the dult femdult fem ere were w pp asas tureture le (Figure 15) and le (Figure 15) and The The oregoreg ionion w, w hichic h wh w asas ocuocu or mor m ed bosted bost frequently frequently ale burrowing owls (eale burrowing owls (e ight timight tim s of the G-test of s of the G-test of upp X ort0.0ort0.0 the5,7) nu= 14 nu= 14 be obs be obs twervtwerv eenatieenati sexon p sexon p 2 (upp X the5,7) owow ls inls in 2 ( F igur e 15 : Be havio r of ad ult female burrowing owls wit y810121410 105911 115912 12591314 145915 155916 165917 175918 185919 195920 20TimeOccurrences thou oung 0246Number of 1359 59 pr eening sca nning vo calizing ther moreg ulation Fig5lt female burrowing owls ure 1 : Be ha vio r of adu without yo un g
53 s on of ut young were similar (Table 13). The ale located at the burrow (0.71). The least frequent transition was from missing to a male located somewhere within the improved pasture (0.29). For females without young the most frequent transition was from missing to a female located at the burrow (0.80). The least frequent transition was from missing to a female being located somewhere within the improved pasture (0.20). During behavioral observations the locations of male and female burrowing owlwithin the improved pasture were similar (Table 12). The results of the G-test of independence supported the null hypothesis of no association between sex and locatiadult burrowing owls without young G = 0.548 < X 2 (0.05, 2) = 5.991. The transition probabilities for adults witho most frequent transition for m ales without young was from missing to a m Figure 16: Behavior of adult male burrowing owls without young1520nces 010 105911 115912 125913 135914 145915 155916 165917 175918 185919 195920 2059Time 5Numbccurre 10er of O preening scanning hunting dozing digging thermoregulation Figure 16: Behavior of adult male burrowing owls without young
Figure 17: Obs Time Date 10 30 15 15:30 16 16:30 17 17:30 18 18:30 19 5/4/04 X X X X X 5/6/04 X X X X X 5/9/04 X X X X 5/12/04 X X X X 5/14/04 X 5/21/04 X 5/25/04 X 5/26/04 X 5/31/04 X X X X 6/2/04 X X X X X 54 19:30 20 X ervation peri 10:30 11 11:30 X X X X X X X X X X X ods (X) for adult 12 12:30 1 X X X X X X X X X X X burrowing owls 3 13:30 14 14: X X X X X X X X X X X X X
Juvenile Burrowing Owls A graph of juvenile burrowing owl behavior is displayed in Figure 18. The observation periods for all juvenile burrowing owls is shown in Figure 19. The most scanning. The second most frequent behavior, observed ten times, was practicing flying. Running into the burrow was the third most frequently observed behavior and was documented eight tim. freq ue ntl y o bse rv ed beh av ior fo r ju ve nil e b urr ow in g o wl s w as es Figure 18: Behavior of juvenile burrowing owls051015202530354010 105115TimeNumber of Occurrences 55 911 912 125 913 13 591 4 1 459 15 1559 16 165 917 175 918 18 591 9 1 959 20 20 59 scanning dozing bei ng fe d by adult vocalizing digging in burrow pra ctice flying stretch wings running into burrow Figure 18: Be hav ior of juv eni le b ur row ing ow ls
Figure 19: Observation periods (X) for juvenile burrowing owls Time 10 10:30 11 11:30 12 12:30 13 13:30 14 14:30 15 15:30 16 16:3 17:30 10 8 18:30 19 19:30 2 0 17 X X X X X X Date X X X X 5/6/04 X X 5/9/04 X X X 5/12/04 X X X X X X X X X 5/14/04 X X X 5/26/04 X X X X X X 5/31/04 X 6/2/04 X 56
Discussion Behavior The most freyoung was scanning. This was expected considering the burrowing owls exposed position in the improved pasture, t need to capture prey, and the numerous potential predators of burrowing owls in the rural habitat. Interestinglt burrowing owls without young, only males were observed digging burrows. Alternatively, for adultsdigging burrows. Both adults are known to ex1993). It is unknown if prior to breeding adult males do the majority of burrow excavation and, after brog young, adult females do the majority of digging in order to maintain burrow structure. The disappearance of males for extended periods of time may account for the observations of only femles field observations male burrowing owls withissing for up to one hour at a time. Forlt burrowiwls without young only males were observed hunting during the daytimle and female burrowing owls raising young were observed hunting. Thedung probably eains the observations of both sexes hunting during the de. Initially the adult mmale is brooding (Hles with young began hunting close to the main burrohen downeathered young were observed in the burrow entrances. As the young grew older, fem hunting trips proceeded to get farther and farther from the main burrows. The behavior of juvenile burrowing owgrowth. At all stages of growth the young were observed scanning the surrounding area. Recently hed covered with downy feathers, spent the majority of time at the adue neaytimaug et al. 1993). In this study, fews watch ng oa e. Both m to fe ed yo xpl a le does all of the hunting while the fe ma y-fale ls was dependent upon their stage of yo un g, quently observed behavior for adult burrowing owls with and without he ly fo r adu raising young, only fe m ales were observed ca vate and m a intain burrows (Haug et al. odin a excavating burrows after brooding. During young were docum ented as m 57
58 he main burrow. As the young grew older, they made excursions farther way from the main burrow. When juvenile plumage began to resemble that of adults, ere observed stretching their wings. As the feathering became more fully oung were s een attempting to fly. res and/ or recently flew from the structure. Also, toward dult burrowing owls were never observed removing prey remains om th burrowing owls with young in the improved pasture were not similar e the main or satellite burrow or somewhere in the improved pasture. entrance of t a juveniles w developed, the y Juvenile burrowing owls appeared to mimic the behavior of nearby adult burrowing owls. Juvenile burrowing owls atte mpted to perch on wooden stakes next to burrow mounds and dog fennel ( Eupatorium capillifolium ) growing in the pasture when an adult was perched on these structu juvenile burrowing owls were twice observed digging in a burrow immediately after an adult was observed digging in the same burrow. Before the young fledged, they began flying with the adult females from the main burrows to satellite burrows. Juvenile burro wing owls were also observed flying adult females that had just captured prey. Interestingly, on 5/14/2004, one juvenile burrowing owl emerged from the main burrow carrying part of a moths wing (species unknown) in its mouth. The chick walked roughly 10 meters from the burrow, dropped the wing into the grass, and then ran back into the main burrow. A fre inside of burrows. Location of Adult Burrowing Owl s and Transition Probability The locations of male and female bu rrowing owls without young in the improved pasture were very similar (Table 12). Ther e was no association between the sex of an adult and the adults location within the impr oved pasture. Alternativ ely, the locations of male and female (Table 12). Where a male or female might be located was dependent on the sex of th owl. The majority of time adult male burrowi ng owls would be found at either the main or satellite burrow or missing. Adult female burrowing owls would be located at either
59 bility of transitioning from ewhere in the im ing from missing to the on probabilities, moving from somewhere in proved pasture to the burrow and transi burrows. Adult females were also observed by dog fennel plants. Females transitioned the shade created by The transition probabilities calculated fo r male and female burrowing owls with young concurs with field observations during the breeding season. Male burrowing owls raising young had a high probability of transitioning from the burrow to somewhere in the improved pasture (0.66). The males also had a high proba som proved pasture to missi ng (0.62). During the breeding season at Rutland Ranch male burrowing owls could be seen flying from the main or satellite burrows and perching on a dog fennel plant, woode n post, or other object in the improved pasture. The adult males would then fly to another perch farther away and this process was repeated until the owl could no longer be located in the improved pasture. Females with young had a high probability of transition burrow (0.86). This may be explained by a dult females being in the burrow during one observation period and then emerging from the burrow at the following observation period. The second and third highest transiti the im tioning from the burrow to somewhere in the improved pasture, agree with field obs ervations. After hatching, the young were commonly seen in the entrance of the burro w or on the burrow mound. During this time it was not uncommon to find females perched on a dog fennel plant or wooden post within roughly 30 meters of the main or satellite perched on the ground in the shade created back and forth from the burrows to either pe rches in the pasture or the perches. For adult burrowing owls raising young there was an association between the sex of an adult and its location in the pasture, but there was no associa tion between the sex of an adult and its behavior during the breeding period. The similarity in behavior between the sexes may be due to the need to feed young during the breeding period. Alternatively, for adult burrowing owls without young there was no association between the sex of an owl and its location in the improved pastur e during the breeding period, but there was an associ ation between the sex of an owl and its behavior. Females without young were observed vocalizing while males without young were never observed
60 ring of e and wing owls by creating a hete rogeneous breeding habitat containing a ixture rds of each of these e vocalizing. Also, males without you ng were observed hunting, dozing, and thermoregulating, while females were never observed exhibiting these behaviors. Male and female burrowing owls may exhibit diffe rent behaviors outside of the breeding season and these behaviors may persist until the female begins brooding young during the breeding period. For example, burrowing owls are thought to shift act ivity patterns du the post-breeding period and become more arboreal (Hoxie 1889), crepuscular, and nocturnal (Hoxie 1889, Mealey 2004 personal communication). Also, during this study, juvenile burrowing owls were not observed with other juvenile or adult burrowing owls during the dispersal and postbreeding period. Therefore, th e colonial behavior burrowing owls may only occur during the breeding period. What effect anthropogenic changes to the improved pasture, such as the introduction of cattle, would have on habitat use of adult burrowing owls during the breeding period is unknown. The observations in this study indicate that adult burrowing owls with young, especially adult males, utilized extensive areas of the improved pastur during the daytime. Adult males were observe d flying hundreds of meters from main satellite burrows before being lost from vi ew. Previous observations of burrowing owls breeding in cattle pastures sugge st that grazing may create suitable breeding habitat for burrowing owls. The use of grazing, prescribed burning, and mowing has been recommended to maintain prairie habitat (Vickery et al. 1999). These land management practices could benefit burro m of short grass areas and non-grazed areas. The short grass areas would be suitable for the excavation of burrows. Areas that havent undergone grazing, burning, or mowing would contain vegetati on that could be use by burrowing owls for both perches and shade. More research needs to be done to determine the benefits and haza land management strategies for burro wing owls. For example, what stocking rat (animals per acre) is optimal to allow bot h cattle and burrowing owls to coexist in pastures? Would a heavily graz ed pasture result in burro w trampling, reduced nesting success, decreased prey availability, or reduced burrow density? When should prescribed
61 t for e the vior will this subspecies. burning or mowing be initiated in order to maintain suitable breeding habita burrowing owls on public land while not negatively affecting reproductive success? Could the time period of prescribed burning (win ter versus spring) de ter or encourag immigration burrowing owls? Much more research is required to u nderstand the behavior and habitat use of burrowing owls in rural areas. Other avenues of research include elucidating the beha and habitat use of burrowing owls in th e evening during the breeding period. Of particular interest is the behavior and habitat use of burrowing owls during the postbreeding period. The successful conservation and management of burrowing owls require understanding the year round habitat requiremen ts of
62 ethods to Capture Burrowing Owls in Florida and ew breeding habitat created in suburban and indus trial areas throughout the state has resulted in numerous research activities. These endea vors have been undertak en to elucidate the demography and ecology of burrowing owls in these new environments. The various management and research ac tivities on burrowing owls in suburban and industrial areas have sometimes require d the capture of this species. Florida burrowing owls have been captured in or der to attach leg bands for individual identification (Courser 1976, Millsap and Bear 1988, Millsap and Bear 1990, Mealey 1997, Millsap and Bear 1997), weighing (Courser 1976, Millsap 1997), measuring (Courser 1976, Mealey 1997), inspection for pa rasites (Courser 1976), and evaluation of feather condition (Courser 1976). Determining wh ich trapping technique to use depends on the effectiveness of previously tested methods and the location of the study. For example, in urban areas the public perception of wildlife management and their participation in creating wildlife management plans may influence the methods used to capture wildlife (Peterso n et al. 2003). Therefore, individuals interested in capturing a species need to determine wh ich trapping method may be the most effective for their particular research (Schemnitz 1996). Various trapping techniques have been us ed in an attempt to capture the western subspecies of burrowing owl ( Athene cunicularia hypugaea ). Some of the methods used include the PVC tube trap (Botelho and Arrowood 1995), padded leg-hold traps (Haug and Oliphant 1990), push-door trap (Winchell 1999), noose rod (Winchell and Turman Evaluation of Three M Introduction Anthropogenic changes to the Florida lands cape has resulted in both the loss creation of burrowing owl breeding habitat (Millsap 1997). The expansion of burrowing owls from rural breeding hab itat in southwestern and s outh-central Florida to n
63 1992), mist nets (Ferguson and Jorgensen 1981) and noose carpet tr aps (Barrentine and Ewing1988). Burrowing owls have also been cap tured within artifici al nest boxes (Todd 2001). F s such as bal-chatri traps (Meale y 1997) and noose carpet traps (Millsap and Bear 1988, Millsap Mealey 1997, Millsap and Bear 1997). Juvenile owls have also been cured by reaching into burrows and capturi ng them by hand (Mealey 1997). There has e lorida. lorida burrowing owls have been captured using variations of leg hold trap and Bear 1990, se been no previous research to evaluate diffe rent methods to capture burrowing owls in Florida. The purpose of this study was to compare one variation of a leg hold trap, th noose carpet, versus two box type traps (PVC tube trap and push-door trap) that have never been used to capture Florida burrowing owls. Determining which type of trap is most effective may aid future studies on burrowing owls in rural areas of F
64 Juvenile burrowing owls were captured in order to attach necklace radio ansmi One end of the PVC tube was cove red with wire mesh to prevent an owl om es r ccording to the methods of Botelho and Arrowood (1995). Two push-door traps were constructe d following the methods detailed by inchell (1999). The traps were constructed of wire mesh fencing and were 46cm long X 5cm wide X 15cm high. One end of the trap was closed to prevent escape. A hinged lexiglas door was placed at the entrance of the trap. It hung at roughly a 45 degree angle to the trap allowing owls to en ter, but not escape (Winchell 1999). Eight noose carpet traps were created using wire mesh. The three trap sizes were 15cm X 10cm, 15cm X 15cm, and 20cm X 10c m. Ten pound monofilament line was used to create the nooses. Drags, made of 57-85 gr am lead weights and attached to the traps with monofilament line, allowed captured ow ls to only fly a short distance before returning to the ground (Barrentine and Ewing 1988, Mealey 2004, personal communication). The PVC tube traps and push-door traps we re set in place when it was known that juvenile burrowing owls were inside the burro ws. The PVC tube traps were placed as far as possible into the burrow. The push-door trap s were placed against the entrance of the burrow. The structure of the burrow entrance and burrow mound were not modified when the traps were set in place. Any open areas created because the trap did not sit flush Methods trtters. All trapping of burrowing ow ls took place in the improved pasture at Rutland Ranch in Bradenton, Florida. Trapping was conducted from 6/6/04 7/12/04 between the hours of 7:30am and 7pm. Two PVC tube traps were constructe d following the methods of Botelho and Arrowood (1995). The traps consisted of PV C tubing that was 16cm in diameter and 61cm long frcaping. The end of the PVC tube ex tending into the burrow had a one way doo made of Plexiglass strips which only swung one way (into the trap). A hinged door, which would be used to remove captured owls was cut into the center of the trap and attached with Velcro tape. The traps were placed into the en trance of the burrows a W 1 P in
65 urrow or against the burrow entr ance were covered with brown burlap cloth. he cloth prevented an owl from escaping the burrow. burrow rrow. ere either inside or outside of the burrow. the ) growing near the burrow, topped walking wls a turning to reducing the possibili ty of capturing juvenile burrowing owls. within the b T Three to five noose carpet traps per burro w were usually placed inside the and on the burrow mound. The traps were easily be nt to contour the inside of the bu Traps were pressed into the sand so only the nooses were exposed. Noose carpet traps were set when juvenile burrowing owls w Before trapping began we placed sma ll unpainted wooden stakes within three meters of the burrow mound for each main burrow (Thomsen 1971). Each stake protruded approximately 30 centimeters from the ground. The stakes were used as perches by the owls and also allowed us to de termine if adults were present at burrows when vegetative growth be gan to obstruct viewing. During behavioral observations we note d that juvenile burrowing owls would quickly emerge from burrows once either ad ult returned to the burrow and stood on burrow mound, perched dog fennel ( Eupatorium capillifolium or perched on the small wooden stake near the burrow mound. We attempted to encourage juvenile burrowing ow ls to exit the burrows by herding adult male or female burrowing owls towards their burrows in which traps were set. This was accomplished by walking around burrows until individual ow ls were located between research personnel and a burrow and then slowly walk ing toward the owl. We s toward an owl when it flew at or near the burrow. This same technique was used to herd any juvenile owls that were outside the bu rrows toward burrows set with noose carpets. In 2004 only three out of the five burro wing owl pairs were observed raising young. Due to the short trapping period and sma ll number of juvenile burrowing o trapping method was discontinued if it deterred adult burrowing owls from re the burrow therefore
66 ile 2:45 pm. Each trap was set in place s on of Time Period Duration of Trapping Number of Juvenile Owls Captured/Recaptured Results One PVC tube trap was set in the main burrow of a burrowing owl pair with young on 6/11/04 at 1pm. A second PVC tube trap was set in the main burrow of another burrowing owl pair with young on 6/20/04 at 9am. Each trap was in place for one hour No juvenile owls were captured during either trapping session. During both trapping sessions the adult male and female burrowing owls would not approach the burrow wh the trap was in place. On 6/6/04, at 9:30 am, one push-door tr ap was set against the main burrow entrance of a burrowing owl pair with young. A second push-door trap was set in the main burrow of another pair with young on 6/7/04 at for one hour. No juvenile owls were captu red in either trapping session. During both trapping sessions the adult male and fema le burrowing owls would not approach the burrow while the trap was in place. I decided to discontinue trapping with PVC tube traps and push-door trap because no juveniles were caught and adults avoided burrows in which traps were set. Only noose carpet traps were us ed to trap juvenile burrowi ng owls for the remainder of the breeding season. Noose carpet traps were used from 6/ 8/04 7/12/04. During each trapping sessi between three and five traps were set at ma in, satellite burrows or both. Adult male and female burrowing owls did not avoid burrows in which traps had been set. Noose carpet traps were set for a total of 30 hours and 35 mi nutes resulting in the capture/recapture eleven juvenile owls. Table 14 indicates the number of burrowing owls captured during three time periods. Table 14. Number of owls captured/recaptured during three time periods. 7am Noon 10 hours and 35 minutes 4 Noon 5pm 15 hours and 30 minutes 7 5pm 9pm 4 hours and 30 minutes 0
67 n e site of the behavior observed when traps were not set at burrows heir ost ef fective method in capturing juvenile rrows nile burrowing owls cap tured at the same time while running into arch of burrowing owls rura l environment may requi re the capture of ective inducement for juvenile burrowing owls to exit the bu s are rec r ca be cause of their ease of transport and effi Discussio The PVC tube traps and push-door traps we re ineffective in capturing juvenil burrowing owls. When in place the PVC tube tr ap and push-door trap protruded from the burrow entrance. During trapping sessions the adult male and female burrowing owls would fly over to the burrows that were trapped, but fly away once the traps were seen The adults would not perch on nearby dog fennel plants or the stake next to the burrow mound. This was oppo and juveniles would readily emerge from burrows upon the return of either adult. Another reason to discontinue using PVC tube traps and push-door traps was t bulkiness. Due to stream flooding it was some times impossible to drive a four wheel drive pickup truck or ATV all the way to th e improved pasture. It was difficult for one individual to carry a trap, plus other research equipment to the improved pasture. Noose carpet traps were the m burrowing owls. Adult male and female burrowi ng owls would readily return to bu in which traps were set. The majority of the time noose carpet traps resulted in the capture of one juvenile burrowing owl per trapping session. Only during one trapping session were two juve the burrow. Another benefit of using noose carpet trap s was the ease of tr ansporting traps to the research area. Each trap and lead drag was place in a separate plastic bag to stop nooses from different traps entangling each other. The traps were quickly set and captured burrowing owls were easily obser ved struggling to free themselves. Further rese individual owls. Herding a dult burrowing owls toward burrows was an eff rrows. Noose carpet trap oo mmended f pturing burrowing owls ciency.
68 aviour ., Elliot, P., Freeman, D. and William VanGelder. 2003. Resource rogram Report: Natural Sy stems 2000-2001. Southwest Florida Water eference al ce I. and John P. Crowder. 1974. An Evaluation of the Extent of Vegetative abitat Alteration in South Florida 1943-1970. U.S. Department of the Interior. Bureau f Sport Fisheries and Wildlife PB-231-621. Pp. 27. References Abrahamson, Warren G. 1984a. Post-Fire R ecovery of Florida Lake Wales Ridge Vegetation. American Jour nal of Botany. 71(1):9-21. Abrahamson, Warren G. 1984b. Species Responses to Fire on the Florida Lake Wales Ridge. American Journal of Botany. 71(1):35-43. Abrahamson, Warren G. and David C. Hartne t. 1990. Pine Flatwoods and Dry Prairies. Pp. 103-149 in Myers, Ronald L. and John J. Ewel, eds., Ecosystems of Florida. University of Central Florida Press, Orlando, Florida. Pp. 765. Altmann, Jeanne. 1974. Observational Study of Behavior: Sampling Methods. Beh 49:227-267. Arnett, Ross H. 2000. American Insects: A Handbook of the Insects of America North of Mexico. Second Edition. CRC Press, Boca Raton, FL. Pp. 1003. Avian Biotech. 2004. Feather Sample Collection. http://www.avianbiotech.com/Feathers.htm viewed 11/4/2004. Barnwell, M Monitoring P Management District. Pp. 196. Barrentine, C. D. and K. D. Ewing. 1 988. A Capture Technique for Burrowing Owls. North American Bird Bander 13:107. Bendire, Charles. 1892. Life Histories of North American Birds with Special R to Their Breeding Habits and Eggs, with Twelve Lithographic Plates. U.S. National Museum, Special Bulleting Number One. Pp. 446. Bent, A.C. 1938. Life Histories of North American Birds of Prey. Part 2. U.S. Nation Museum Bulletin. No 170. Pp. 482. Birnhak, Bru H o
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The florida burrowing owl in a rural environment
h [electronic resource] :
b breeding habitat, dispersal, post-breeding habitat, behavior, and diet /
by Robert Mrykalo.
[Tampa, Fla.] :
University of South Florida,
Thesis (M.S.)--University of South Florida, 2005.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
System requirements: World Wide Web browser and PDF reader.
Mode of access: World Wide Web.
Title from PDF of title page.
Document formatted into pages; contains 84 pages.
ABSTRACT: The first observations of Florida burrowing owls (Athene cunicularia floridana) occurred in the 19th century on historical dry prairie habitat in south central Florida. These early observations documented the ecology of burrowing owls in rural environments. Since then the vast majority of research on this subspecies has been undertaken in suburban and urban environments during the breeding period. The research undertaken on burrowing owls in suburban and urban environments includes determining natal dispersal distance, assessing female fecundity, mate fidelity, territory fidelity, date of juvenile and adult dispersal from breeding habitat, date of clutch initiation, nesting success, density of breeding pairs, causes of mortality, prey preference, and minimum annual survival of fledglings, juveniles, and adults. Very little research has been undertaken on burrowing owls in rural environments.The purpose of this thesis was to elucidate the behavior and ecology of burrowing owls in a rural environment. The topics researched in this thesis include home range in breeding habitat, dispersal distance to post-breeding habitat, location of post-breeding habitat, behavior during the breeding period, diet of rural versus urban owls, and the evaluation of three methods to trap burrowing owls. The results of this thesis indicate that, during the daytime, juvenile burrowing owls utilized habitat very close to the main and satellite burrows during the breeding period. At night juvenile owls foraged in an extensive saw palmetto patch surrounding the breeding habitat. The predominant prey of both rural and urban burrowing owls during the breeding period was insects. Dispersal of juvenile burrowing owls from breeding habitat coincided with the flooding of the breeding habitat during the rainy season.
Adviser: Dr. Melissa Grigione.
Athene cunicularia floridana.
Species of special concern.
x Environmental Science and Policy
t USF Electronic Theses and Dissertations.