|USFLDC Home | Tropical Ecology Collection [Monteverde Institute]||| RSS|
This item is only available as the following downloads:
xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xlink http:www.w3.org1999xlink xmlns:xsi http:www.w3.org2001XMLSchema-instance
leader 00000nas 2200000Ka 4500
controlfield tag 008 000000c19749999pautr p s 0 0eng d
datafield ind1 8 ind2 024
subfield code a M39-00168
Prahl, Lili K.
Determinando la vulnerabilidad aviar a los ectoparsitos usando rasgos morfolgicos y de historia natural
Determining avian vulnerability to ectoparasites using morphological and natural history traits
Avian parasitism is the cause of many negative effects on host organisms including decreased fitness through reproductive failure and reduced health. There is increasing research being done to assess the characteristics of bird host morphology and natural history that influence the presence and abundance of ectoparasites on these hosts. This study attempts to create an index of sensitivity that can be used for different bird species in order to determine their expected vulnerability to ectoparasites. This index uses five parameters: bird weight and bill length, both determined by field work, as well as bird behavior, habitat, and population density. This index was then compared to data collected that determined the presence of mites in seven different bird species of Monteverde, Costa Rica. The index proved to be accurate for the most extreme cases but failed to accurately predict the presence of ectoparasites in bird species in the middle range of the index.
El parasitismo en las aves es la causa de muchos efectos negativos en estos organismos. De esto deriva la importancia de investigar si las caractersticas morfolgicas y la historia de la especie de ave influyen en la presencia y la abundancia de ectoparsitos en estos anfitriones. Este estudio procura crear un ndice de sensibilidad que puede ser utilizada para determinar la vulnerabilidad esperada a los ectoparsitos en las diferentes especies de aves.
Text in English.
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology
Determining avian vulnerability to ectoparasites using morphological and natural history traits Lili K. Prahl Department of Wildlife Ecology, Un iversity of WisconsinMadison ABSTRACT Avian parasitism is the cause of many negative effects on host organisms including decreased fitness through reproductive failure and reduced health. There is increasing research being done to assess the characteristics of bird host morphology and natural history that influence the pres ence and abundance of ectoparasites on these hosts. This study attempts to create an index of sensitivity that can be used for different bird species in order to determine their expected vulnerability to ectoparasites. This index uses five parameters: bird weight and bill length, both determined by field work, as well as bird behavior, habitat, and population density. This index was then compared to data collected that determined the presence of mites in seven different bird species of Monteverde, Costa Rica. The index proved to be accurate for the most extreme cas es but failed to accurately predict the presence of ectoparasites in bird species in the middle range of the index. RESUMEN El parasitismo en las aves es la causa de muchos efectos negativos en estos organismos. De sto deriva la importancia de investigar si las charactersticas morfolgicas y la historia de la especie de ave influye en la presencia y la abundancia de ectoparasitos en estos anfitrione s. Este estudio procura crear un ndice de sensibilidad que puede ser utilizada para determinar la vulnerabilidad espe rada a ectoparastios en las diferentes especios de aves. Este ndice utiliza cinco parmetros: el peso de pjaro y longitud de pico, el compartamiento social, el habitat, la densidad poblacional. Este ndice fue aplicado a siete especi es de aves in Monteverde, Co sta Rica. El ndice result exacto para los casos ms extremos en las especies pero fall en la prediccin de la presencia de ectoparasitos en los valores medios ndice. INTRODUCTION Parasitism is thought to influence many aspects of avian ecology including fitness (Brown & Brown 2002) and population dynamics (Brown and Brown 2004). Two kinds of ectoparasites that are often found on birds are mites (subcla ss Acari) and lice (suborders Amblycera and Ishnocera). Because of their ne gative effects on their hosts stemming from nutrient depletion, increased feather asymmetry, and, in some cases, in creased rate of infect ion, these ectoparasties are thought to impact the survival and fitness of their hosts (Brown & Brown 2002). There are several factors that are tho ught to influence the abundance of avian ectoparasites for different bird species (Clayt on & Walther 2001). These include, but are not limited to, bird size, bill length, be havior, habitat, and host density. Bird size has been shown to play a role in ectoparasite loads with larger birds having larger ectopara site loads (Clayton and Walther 2001). This is thought to be because they have larger resource bases for parasites. Bill length may have an effect on parasite load by influencing the effectiveness of grooming and removing parasites (Cotgreave & Clayton 1994). Beha vior in terms of sociality has also been 1
shown to affect ectoparasite lo ads in the case of some bird sp ecies (Whiteman & Parker 2004). More social birds, because of increased horizonta l transmission of parasite s, have been shown to have higher abundances of ectoparasites (Whitema n & Parker 2004). Microhabitat can have an effect on parasite abundance as well (Read 1991). It is thought that birds that forage lower to the ground will have higher ectoparasite loads than thos e that forage in the canopy because there is an increased abundance of parasites found in ve getation at those hei ghts (Pruett-Jones and Pruett-Jones 1991, in Clayton and Walther 2001). Host density can also be used to determine the abundance of ectoparasites in bird species. It has been shown that bird populations with higher densities have higher parasite lo ads than those with lower dens ities (Tella et al. 1999). Using the above parameters, I compiled an index of sensitivity that will potentially predict a hosts vulnerability to ectoparasites. Using this index of sensitivity, I will be able to determine the likelihood and abundance of pa rasites on a given host using easily attainable natural history information. This study attempts to test the po tential for such an index of sensitivity in predicting ectoparasite presence a nd abundance. It also attempts to find a threshold value or range over which ectoparasite presence is assu red and below which ectoparasite absence is assured. MATERIALS AND METHODS Study Site and Bird Species I conducted this study in the lower montane wet fo rest at the Estacin Bi olgica de Monteverde in Monteverde (1535 m) and the fragmented secondary forest at the Finca Santamara in Caitas (1300 m), Puntarenas, Costa Rica. Th e study took place between October 30th and November 17th, 2006. Seven different bird species were studied: White-eared ground sparrow, Melozone leucotis (Emberizidae), Long-tailed manakin, Chiroxiphia linearis (Pipridae), Striped-tailed hummingbird, Eupherusa eximia (Trochilidae), Purple-throated mountain-gem, Lampornis calolaema (Trochilidae), Violet Sabrewing, Campylopterus hemileucurus (Trochilidae), Green violet-ear, Colibri thalassinus (Trochilidae), and Scintillant hummingbird, Selasphorus scintilla (Trochilidae). Data Collection Hummingbird feeders were set up along forest edges at both study sites. Th ey were filled with a 28% sugar solution and allowed to hang without disturbance for two to five days, which gave the hummingbirds time to find them. After that time a twelve meter or a twelve meter and a six meter mist net were set up near the feeders at th e forest edge. The mist nets were opened from 7:30-11:30 am for a total of seven days between the two locations. The nets were continuously monitored from a distance of approximately ten meters. When a hummingbird flew into the net and became trapped it was immediately rem oved, identified, and analyzed for data. To catch other kinds of bird species from fo rest edge habitats, six and twelve meter mist nets were set up in the different locations for a total of six days. Sites were chosen near the forest edge along trail edges. These nets were checked for birds every ten minutes. If a bird was caught, it was removed, identified, and analyzed. Only the site in Caitas yielded samples. After birds were removed from the mist nets, they were analyzed for a variety of different parameters. First, in the case of the hummingbirds, I measured th eir bill length using calibers. 2
Then, for all birds studied, they were analyzed fo r ectoparasite presence. I used a paintbrush to brush the feathers of the bird while it was posit ioned above a circle of wax paper. The wax paper was meant to catch whatever was brushed off of the bird. An effort wa s made to brush every part of the birds body including th e head, back and rump, in orde r to obtain the highest number of ectoparasites. New brushes were used with every species type to prevent contamination ensure that any ectoparasties found were only from that species. Then its face and bill were visually examined for mite presence. Finally, the bird was weighed in a cloth bag using a 100 g pesola scale before being released. The ectoparasites were preserved in a glass vi al with 70% ethanol, and pooled by species. To analyze the number of parasites in each specie s, the ethanol from each vial was poured into a 5.5 cm Petri dish. Each Petri dish was analyzed for 30 minutes using a dissecting microscope by visually searching for any intact ectoparasite bodies. Analysis I created an index of sensitivity to ectoparasites using the data collected in the study and natural history information (Stiles and Skutch 1989). Th e five parameters mentioned previously were used in order to compile this index. Each parameter was assigned a number value depending on its importance as a determinant of ectoparasite vulnerability. Each bird species was then analyzed for their standing within each parameter and assigned a value based on that. To make the index, the values of each parameter were a dded together and that number was divided by the total number of points possible and then multiplied by 10. 1.) Weight: This was used as a measure of bi rd size and was assigned a relative importance of three. The data collected were analy zed using a one-way ANOVA and a Post Hoc test to see what species were significantly different in weight than the others. Only species with more than one data point were used, and the other species were ranked according to their relative values. According to the result s of these analyses and the rankings using relative means each species was assigned a point value with zero being the smallest and three being the largest. 2.) Habitat: Habitat was assigned a relative impor tance of three. Species were given one point for dwelling in forest edges. Two more points were given to ground foraging birds, one point was given understory birds, and zero points were given to mostly canopy dwelling species. 3.) Behavior: Behavior was assigned a relative importance of two. Social species were given a value of two, species that were paired or engaged in leking behavior and were in their breeding season were given a value of one, and solitary birds that were out of breeding season were given a value of zero. 4.) Bill Length: This parameter was only used for hummingbirds and was assigned a relative importance of one. The data collected were analyzed using a one-way ANOVA and Post Hoc test to see if there was a significant di fference in bill length between the species. Once again only the bird species with more than one data point were used in this analysis, and the others were ranked according to their relative values. A one-way ANOVA with weight as a covariate was used to eliminat e the possible effect of mass on the effective bill size. Each species was then assigned a value with zero being the smallest and one being the largest bill size. 3
5.) Distribution: Distribution wa s assigned a relative significan ce of one. Common species in lower montane wet forest were given a value of one, fairly common a value of 0.5 and rare a value of zero. RESULTS Field Data Five mites were found in only four of the seven sp ecies studied and lice coul d not be detected in any of the species. Species with mites incl uded the white-eared ground sparrow, the stripedtailed hummingbird, the purple-throated mountain-ge m, and the long-tailed manakin (Table 1). The mites found were ectoparasites and not m ites involved in phoresy, which is common in hummingbirds. Weight was found to be significantly different between all species except for between the striped-tailed hummingb ird and the purple-throated mountai n gem (F=954.869; df effect=3; df error=15; p-level=0.000) (Figure 1). The wh ite-eared ground sparrow was found to be the heaviest followed by the violet sabrewing. The striped-tailed hummingbird and the purplethroated mountain-gem were the smallest. Using relative means, the green violet-ear was placed in the same weight class as the striped-tail ed hummingbird and the purple-throated mountaingem. The long-tailed manakin was placed in a ranking in between the white-eared ground sparrow and the violet sabrewing. The scintillan t hummingbird was ranked the lowest in mass. Bill length was found to be significantly different between all hummingbird species tested and the violet sabrewi ng (F=165.6917; df effect=2; df erro r=14; p-level=0.000) (Figure 2). Using relative means the green violet-ear and th e scintillant hummingbird were found to be in the same weight class as all th e other hummingbirds, except for th e violet sabrewi ng. The violet sabrewing had the longest bill and the scintillan t had the smallest. These results were found to be the same even when using weight as a c ovariate (F=21.26911; df effect=4; df error=13; pvalue=0.000). Index of Sensitivity Using this index, the most sensitive study speci es to ectoparasites was found to be the whiteeared ground sparrow, followed by the violet sabrewing, and the long-tailed manakin. Then came the green violet-ear, the striped tailed hum mingbird and the purple-th roated mountain-gem, which were rated the same on the index and were followed by the scintillant hummingbird, which had the least sensitivity (Table 1). If we consider the mite presence in the white-eared ground sparrow, the scintillant hummingbird and the long-tailed manakin to be correlated well with our index, and the rest of the bird species not to be, the index has a success rate of 42.8%. DISCUSSION Using the parameters outlined, the index of sensitivity for avian ectoparasites would be expected to correlate with field data on abundance of parasites in a given bird species. This, however, was not found to be the case. While the index of se nsitivity did predict ectoparasite presence for the two most extreme cases, the white-eared ground sparrow and the scintillant hummingbird and had a 42.8% success rate, it failed to give a clear threshold value or range for which ectoparasite 4
presence or absence is assured. This could be for a variety of reasons both biological and methodological. Biologically speaking, it is quite possible that no clear combination of factors is responsible for bird susceptibility to ectoparasi tes. As with everything in ecology, there are many factors contributing to such vulnerability and the index could have easily overlooked some of these factors. For example, host geographic range could play a role in host sensitivity. The bigger a geographic range, the more susceptible a population could be to ect oparasites. This is because the more widespread a host is the higher its probability is for picking up new parasites through host transfer (Tella et al. 1999). There are other characteristics as well that were not taken into consideration when making the index of sensitivity that could have significant impacts on host susceptibility. These include, but are not limited to, beak shape, plumage depth, and foot characteristics (Clayton & Walther 2001). Finally, temporal trends have been found to play a role in ectoparasite abundances, and because of the shortness of this study, the full scope of these effects could not be seen (Dietsch 2005). A problem in methodology could also have an influence in the inaccuracy in the middle range of the index. Despite the fact that birds were captured at forest edges where parasite density is thought to be greatest, I found very few ectoparasites on any of the species (Nadkarni and Wheelwright 2000). Previous studies have used the inse cticide pyrethrin to remove ectoparasites from live birds (Clayton & Drown 2001) or sacrificed birds to get an accurate count of ectoparasites (Clayton & Walther 2001). Because of the small scope of this study and a desire to cause no harm to the birds, it was decide d to employ a different technique that was less successful at obtaining lice and perhaps less accura te when obtaining mites. Therefore the index might be more accurate than the data show because so few mite and no lice samples were collected from any of the birds. Future studies should examine these parameters more closely in order to determine their relative importance in creating such an index. Also, a more accurate method should be employed in order to obtain better data conc erning the number of ectoparasites in individual birds. Overall, the avian ectoparasite sensitivity index created in this study using various natural history and morphological factors is plausible, but more data need s to be collected in order to prove the accuracy of this index before it can be used in further research. ACKNOWLEDGEMENTS Thank you to the Estacin Biolgica de Monteverde and to the Santamara family for allowing me to use their land as my study site. Thank you to Elenia and the Santamara children for keeping me company while I waited for birds. I would like to extend many thanks to Tania for being so supportive in helping me in every step of my project and for helping me with mist-netting both at the station and Caitas (in spite of bad bird karma). I would also like to thank Karen Masters for reassuring me when I thought all was lost on multiple occasions. Many thanks to Alan Masters for making this experience so am azing and for making me smile on a regular basis. To the best TAs in the universe, Camryn Pennington and Tom McFarland, thank you so much for all of your technical help, bad jokes, and mental support throughout the past three months. A speci al thanks to Stephanie Siemek for keeping me company and keeping me sane during my study and to Katie Puzio for working with me to catch hummingbirds. Also, thank you to Stephanie and Katharine Lulling your amazing editing abilities. Finally, thank you to all of my fellow students who make me laugh when it should not be possible and who have helped me get through all of the work and challenges we have faced here. LITERATURE CITED 5
Brown, C.R. and M.B. Brown. 2002. Ectoparasites cause increased bilateral as ymmetry of naturally selected traits in a colonial bird. J. Evol. Biol 15: 1057-1075 Brown, C.R. and M.B. Brown. 2004. Group size and ectoparasitism affect daily survival probability in a colonial bird. Behav Ecol Sociobiol 56: 498-511 Clayton, D.H. and B.A. Walther. 2001. Influence of host ecology and morphology on the diversity of Neotropical bird lice. OIKOS. 94: 455-467 Clayton, D.H. and D.M. Drown. 2001. Critical evaluation of five methods for quantifying chewing lice. J. Parasitol. 87(6): 1291-1300 Cotgreave, P. and D.H. Clayton. 1994. Comparative analysis of time spent grooming by birds in relation to parasite load. Behaviour 131: 171-187 Dietsch, T.V. 2005. Seasonal variation of infestation by ectoparasitic chigger mite larvae on resident and migratory birds in coffee agroecosystems of Chiapas, Mexico. J. Parasitol 91(6): 1294-1303 Nadkarni, N.M. and N.T. Wheelwright. 2000. Monteverde: Ecology and Conservation of a tropical cloud forest. Oxford University Press, New York, NY p. 422 Pruett-Jones, M. and S. Pruett-Jones. 1991. Analysis and ecological correl ates of tick burdens in a New Guinea avifauna. In: Loye, J.E. and M. Zuk (editors), Bird-parasite interactions: ecology, evolution, and behaviour. Oxford University Press, pp. 154-176 Clayton, D.H. and B.A. Walther. 2001. Influence of host ecology and morphology on the diversity of Neotropical bird lice. OIKOS. 94: 455-467 Read, A.F. 1991. Passerine polygyny: a role for parasites? Am. Nat. 138(2): 434-459 Stiles, F.G. and A.F. Skutch. 1989. A Guide to the Birds of Costa Rica. Comstock Publishing Associates, Ithaca, NY. Tella, J.L. G. Blanco, M.G. Forero, A. Gajn, J.A. Donzar, and F. Hiraldo. 1999. Habitat, world geographic range, and embryonic development of hosts explain the prevalence of avian hematozoa at small and phylogenetic scales. Proc. Natl. Acad. Sci. 96: 1785-1789 Whiteman, N.K. and P.G. Parker. 2004. Effect of host sociality on ectoparasite population biology. J. Parasitol 90(5): 939-947 6
Table 1 Determination of the Index of Sensitivity fo r seven species of birds. Weight and bill length rankings determined from ANOVA analyses Habitat and behavior information is from Stiles & Skutch 1989. Distribution was determ ined using Nadkarni & Wheelwright 2000. Species Weight (g) Bill length (mm) Habitat Preference Behavior Distribution Index of Sensitivity Mite Presence White-Eared Ground Sparrow (n=2) 44 g (3) N/A Forest edges, forages on the ground (3) Paired year-round (1) Common (1) 8.89 Yes V iolet Sabrewing (n=6) 10.8 g (1.5) 31.6 mm (1) Forest edges; Forages in the understory (2) Leks; in breeding season (1) Common (1) 6.5 No Long-Tailed Manakin (n=1) 18.5 g (2.25) N/A Forest edges; Forages in the understory (2) Not social out of breeding season (0) Common (1) 5.83 Yes Green Violet-Ear (n=1) 5 g (0.75) 21 mm (0.5) Forest edges; Forages in the understory (2) Loose lekking behavior; in breeding season (1) Common (1) 5.25 No Striped-tailed Hummingbird (n=7) 5.14 g (0.75) 19.6 mm (0.5) Forest edges; Forages in the canopy (1) Not social (0) Common (1) 3.25 Yes Purple-Throated Mountain-Gem (n=4) 4.75 g (0.75) 18.8 mm 0.5 Forest edges; Forages in the canopy (1) Not social (0) Common (1) 3.25 Yes Scintillant Hummingbird (n=1) 2 g (0) 22 mm (0.5) Forest edges; Forages in the understory (2) Not social (0) Fairly common (0.5) 3.0 No 7
Std. Dev. Std. Err. MeanBird SpeciesW e ig h t ( g ) 0 10 20 30 40 50 Striped-tailed Hummingbird Purple-throated Mountain-Gem Violet Sabrewing White-eared ground sparrow Figure 1. Results from ANOVA analysis of bird weight. The viol et sabrewing and white-eared ground sparrow significantly differed from each other and from the othe r two bird species in weight. (F=954.8369; df effect=3; df error=15; p-level=0.000) 8
Hummingbird SpeciesBill length (mm) 16 20 24 28 32 36 Striped-tailed Hummingbird Purple-Throated Mountain Gem Violet Sabrewing Std. Dev. Std. Err. Mean Figure 2. Results from the ANOVA analysis of b ill length for hummingbirds. Significant differences were found between the violet sabrew ing and every other species. Similar results were found when analyzed with weight as a covariat e. (F=165.6917; df effe ct=2; df error=14; plevel=0.000) 9