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Behavioral plasticity in detection height of an invasive, arboreal snake based on size, condition, and prey

Melia Nafus , Levi Gray, Page Klug , Gordon Rodda, Scott Goetz

Abstract

Context: Animals may adjust their behavior in predictable ways to balance tradeoffs between resource acquisition and survival or fecundity. Microhabitat selection based on individual traits or environmental conditions is one measure of risk-reward tradeoffs by individuals. Aims: We used data from observational and manipulative studies to investigate whether an arboreal snake (brown treesnake, Boiga irregularis) had context dependent behavior based on the relationship between estimated prey availability, body condition, size, and detection height (microhabitat use) in two Mariana Islands. Methods: We used observational data collected in four study sites and data from a manipulative study that we collected over a five-year period. The observational data focused on four sites with different counts of three prey types, including lizards, birds, and small mammals. During the manipulative study we removed snakes, which resulted in increased prey counts over time. Using these two approaches, we tested whether prey counts predicted body condition and then evaluated how prey counts, snake size, and snake condition interactively predicted the detection height of captured individuals. Key results: We found that body condition was greater at sites or in years with greater prey counts across both the observational and manipulative studies. We also found that snakes displayed differential microhabitat use based on both their condition and size. Larger snakes tended to be detected lower than smaller snakes, but only at sites or during years with few bird or small mammal counts. Snakes at sites with greater mammal and bird counts had a positive relationship between size and detection height. Snakes with greater condition scores tended to be detected higher irrespective of size, but this was also dependent on prey counts. At sites with low bird counts, snakes that were in better condition tended to be closer to the ground. Conclusions: Brown treesnakes modified microhabitat use based on their condition, size, and the number or type of prey available. Our findings were consistent with a hypothesis that they optimized habitat use to secure food resources and maximize survival. Implications: Context-dependent behavioral plasticity may be an important consideration for management of reptiles for population control or growth.

WR24085  Accepted 04 March 2025

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