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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
1 Determining avian vulnerability to ectoparasites using morphological and natural history traits Lili K. Prahl Department of Wildlife Ecology, University of Wisconsin Â€ Madison ABSTRACT Avian parasitism is the cause of many negative effects on host org anisms 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 ectoparasite s 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 de termined 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 accu rate for the most extreme cases but failed to accurately predict the presence of ectoparasites in bird species i n the middle range of the index . RESUMEN El parasitismo en las aves es la causa de muchos efectos negativos en estos organismos. De esto d eriva la importancia de investigar si las caracterÃsticas morfolÃ³gicas y la historia de la especie de ave influyen en la presencia y la abundancia de ectoparÃ¡sitos en estos anfitriones. Este estudio procura crear un Ãndice de sensibilidad que puede ser ut ilizada para determi nar la vulnerabilidad esperada de los ectoparÃ¡sitos en las diferentes especies de aves. Este Ãndice utiliza cinco parÃ¡metros: el peso de pÃ¡jaro y longitud de pico, el comportamiento social, el hÃ¡bitat , la densidad poblacional. Este Ãndice fue apl icado a siete especies de aves e n Monteverde, Costa Rica. El Ãndice resultÃ³ exacto para los casos mÃ¡s extremos en las especies pero fallÃ³ en la predicciÃ³n de la presencia de ectoparÃ¡sitos en los valores medios Ãndice. INTRODUCTION Parasitism i s 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 subclass Acari and lice suborders Amblycera a nd Ishnocera. Because of their negative effects on their hosts stemming from nutrient depletion, increased feather asymmetry, and, in some cases, increased rate of infection, these ectoparasites are thought to impact the survival and fitness of their hos ts Brown & Brown 2002. There are several factors that are thought to influence the abundance of avian ectoparasites for different bird species Clayton & Walther 2001. These include, but are not limited to, bird size, bill length, behavior, habitat, a nd host density. Bird size has been shown to play a role in e ctoparasite loads with larger birds having larger ectoparasite loads Clayton and Walther 2001. This is thought to be because they have larger resource bases for parasites. Bill length may ha ve an effect on parasite load by influencing the effectiveness of grooming and removing parasites Cotgreave & Clayton 1994. Behavior in terms of sociality has also been shown to affect ectoparasite loads in the case of some bird species Whiteman & Park er 2004.
2 More social birds, because of increased horizontal transmission of parasites, have been shown to have higher abundances of ectoparasites Whiteman & 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 those that forage in the canopy because there is an increased abundance of parasites found in vegetation at those heights Pruett Jones and Pruett Jones 1991, in C layton 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 loads than those with lower densities Tella et al. 19 99. Using the above parameters, I compiled an index of sensitivity that will potentially predict a host s vulnerability to ectoparasites. Using this index of sensitivity, I will be able to determine the likelihood and abundance of parasites on a given host using easily attainable natural history information. This study attempts to test the potential for such an index of sensitivity in predicting ectoparasite presence and abundance. It also attempts to find a threshold value or range over which ectopar asite presence is assured and below which ectoparasites absence is assured. MATERIALS AND METHODS Study Site and Bird Species I conducted this study in the lower montane wet forest at the EstaciÃ³n BiolÃ³gica de Monteverde in Monteverde 1535 m and the f ragmented secondary forest at the Finca SantamarÃa in CaÃ±itas 1300 m, Puntarenas, Costa Rica. The study took place between October 30 th and November 17 th , 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, Gre en 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. They 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 the 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 removed, identified, and analyzed for data. To catch other kinds of bird species from forest 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 CaÃ±itas 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 their bill length using calibers. Then, for all birds studied, they were analyzed for ectoparasite presence. I used a paintbrush to
3 brush the feathers of the bird while it was positioned above a circle of wax paper. The wax paper was meant to catch whatever was brushed off of the bird. An effort was made to brush every part of the bird s body including the head, back and rump, in order to obtain the highest number of ectoparasites. New brushes were used with e very species type to prevent contamination ensure that any ectoparasites 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 be ing released. The ectoparasites were preserved in a glass vial with 70% ethanol, and pooled by species. To analyze the number of parasites in each species, the ethanol from each vial was poured into a 5.5 cm Petri dish. Each Petri dish was analyzed for 3 0 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 . The 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 sta nding within each parameter and assigned a value based on that. To make the index, the values of each parameter were added 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 bird size and was assigned a relative importance of three. The data collected were analyzed 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 results of these analyses and the rankings using relative means each species was assigned a point value with zero being the smallest and three be ing the largest. 2. Habitat: Habitat was assigned a relative importance 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 gi ven 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 lekking 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 difference 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 eliminate 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.
4 5. Distribution: Distribution was assign ed a relative significance 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 species studied and lic e could not be detected in any of the species. Species with mites included the white eared ground sparrow, the striped tailed hummingbird, the purple throated mountain gem, and the long tailed manakin Table 1. The mites found were ectoparasites and not mites involved in phoresy, which is common in hummingbirds. Weight was found to be significantly different between all species except for between the striped tailed hummingbird and the purple throated mountain gem F=954.869; df effect=3; df error=15; p level=0.000 Figure 1. The white eared ground sparrow was found to be the heaviest followed by the violet sabrewing. The striped tailed hummingbird and the purple throated mountain gem were the smallest. Using relative means, the green violet ear was placed in the same weight class as the striped tailed hummingbird and the purple throated mountain gem. The long tailed manakin was placed in a ranking in between the white eared ground sparrow and the violet sabrewing. The scintillant hummingbird was ra nked the lowest in mass. Bill length was found to be significantly different between all hummingbird species tested and the violet sabrewing F=165.6917; df effect=2; df error=14; p level=0.000 Figure 2. Using relative means the green violet ear and the scintillant hummingbird were found to be in the same weight class as all the other hummingbirds, except for the violet sabrewing. The violet sabrewing had the longest bill and the scintillant had the smallest. These results were found to be the same even when using weight as a covariate F=21.26911; df effect=4; df error=13; p value=0.000. Index of Sensitivity Using this index, the most sensitive study species to ectoparasites was found to be the white eared ground sparrow, followed by the viole t sabrewing, and the long tailed manakin. Then came the green violet ear, the striped tailed hummingbird and the purple throated mountain gem, which were rated the same on the index and were followed by the scintillant hummingbird, which had the least sen sitivity 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 th e index of sensitivity 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
5 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 ectoparasites. 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, th e more susceptible a population could be to ectoparasites. 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 we re 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 inaccur acy 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 insecticide 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 decided to employ a different technique that was less successful at obtaining lice and perhaps less accurate when obtaining mites. Therefore the index might be more accurate than the data show because so few mite and no lice samples wer e 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 needs 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 EstaciÃ³n BiolÃ³gica de Monteverde and to the SantamarÃa family for allowing me to use their land as my study site. Thank you to Elen a and the Santam arÃa 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 CaÃ±itas 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 amazing and for making me smile on a regular basis. To the best TA s 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 special 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 an d who have helped me get through all of the work and challenges we have faced here.
6 LITERATURE CITED Brown, C.R. and M.B. Brown. 2002. Ectoparasites cause increased bilateral asymmetry 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. 876: 1291 1300 Cotgreave, P. and D.H. Clayton. 1994. Comparative anal ysis of time spent grooming by birds in relation to parasite load. Behavior . 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 . 916: 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 an d ecological correlates of tick burdens in a New Guinea avifauna. In: Loye, J.E. and M. Zuk editors, Bird parasite interactions: ecology, evolution, and behavior . 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. 1382: 434 459 Stiles, F.G. and A.F. Skutch. 1989. A Guide to the Birds of Costa Ric a. Comstock Publishing Associates, Ithaca, NY. Tella, J.L. G. Blanco, M.G. Forero, A. GajÃ³n, J.A. DonÃ¡zar, 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 . 905: 939 947
7 Table 1 . Determination of the Index of Sensitivity for se ven species of birds. Weight and bill length rankings determined from ANOVA analyses. Habitat and behavior information is from Stiles & Skutch 1989. Distribution was determined using Nadkarni & Wheelwright 2000. Species Weight g Bill length mm Ha bitat 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 Violet Sabrewing n=6 10.8 g 1.5 31.6 mm 1 F orest 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 so cial 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 unders tory 2 Not social 0 Fairly common 0.5 3.0 No
8 Figure 1. Results from ANOVA analysis of bird weight. The violet sabrewing and white eared ground sparrow significantly differed from each other and from the other two bird species in weight. F=954.8369; df effect=3; df error=15; p level=0.000 Â€ Std. Dev. Â€ Std. Err. Mean Bird Species Weight g 0 10 20 30 40 50 Striped-tailed Hummingbird Purple-throated Mountain-Gem Violet Sabrewing White-eared ground sparrow
9 Figure 2. Results from the ANOVA analysis of bill length for hummingbirds. Significant differences were found between the violet sabrewing and every other species. Similar results were found when analyzed with weight as a covariate. F=165.6917; df effect=2; df error=14; p level=0.000 Hummingbird Species Bill length mm 16 20 24 28 32 36 Striped-tailed Hummingbird Purple-Throated Mountain Gem Violet Sabrewing Â€ Std. Dev. Â€ Std. Err. Mean