Ecological Factors Associated With Songbird and Small Mammal Predation by Texas Ratsnakes
Sperry, Jinelle Hutchins
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https://hdl.handle.net/2142/87015
Description
Title
Ecological Factors Associated With Songbird and Small Mammal Predation by Texas Ratsnakes
Author(s)
Sperry, Jinelle Hutchins
Issue Date
2008
Doctoral Committee Chair(s)
Weatherhead, Patrick J.
Department of Study
Ecology, Evolution and Conservation Biology
Discipline
Ecology, Evolution and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Ecology
Language
eng
Abstract
Predator-prey relationships have received extensive theoretical and empirical attention although the majority of studies have focused exclusively on prey. In studies of avian ecology, predation is the primary cause of nest failure and yet few studies examine predators directly. For my dissertation, I used radio-telemetry to monitor Texas ratsnake (Elaphe obsoleta ) habitat use and behavior to examine predation risk on nests of two endangered bird species breeding at Fort Hood, Texas. In addition, a drought occurred which allowed me to examine effects of fluctuating prey abundance on ratsnake condition and survival. I included information from 62 ratsnakes, 880 Black-capped Vireo (Vireo atricapilla) nests, and 228 Golden-checked Warbler (Dendroica chrysoparia) nests. I found that snakes exhibited habitat selection at multiple spatial scales, although the hypothesis that snakes chose habitats based on prey abundance (small mammals and birds) was only weakly supported. Snakes were only selective during winter when foraging was at a minimum and did not shift habitats to target birds' nests during the bird breeding season. Additionally, snakes predominantly ate small mammals, even during peak of the bird-breeding season. Collectively, these results suggest that snake predation on birds' nests is largely opportunistic. On a micro-habitat scale, snakes chose more structured habitats although I did not find a clear relationship between snake habitat preference and avian nest survival. Nest tree characteristics were important for warblers whereas timing of breeding was most important for vireo nest survival. Results indicate that snakes preferentially use warbler habitat and primarily use vireo habitat for foraging. Accordingly, seasonal patterns of vireo daily nest survival were strongly coupled to snake activity. Warbler nest survival was also negatively related to snake activity although the association was less pronounced. These results provide support for the hypothesis that predator behavior can drive avian nest survival although the strength of relationship is species-specific. Finally, I document how a 21-month drought reduced vegetation and small mammal abundance, and the associated decline in ratsnake body condition and survival. Our results indicate than an increase in drought severity or length, as predicted by global warming models, could have pronounced implications for ecosystem health.
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