Open Access Senior Honors Thesis
A particular reaction to a given predator is dependent on the level of danger perceived by an animal. American Goldfinches (Carduelis tristis) are preyed upon by highly threatening predators that commonly attack songbirds at feeders (feeder predator) and less threatening predators that rarely attack songbirds at feeders (non-feeder predators). This study measured the behavioral and vocal reactions of American goldfinches to these different levels of predatory threat and examined the effect of threat level on the trade-off between foraging and anti-predatory behaviors (vigilance). We hypothesized that if goldfinches respond to predatory cues based on the level of threat associated with a particular predator species, then goldfinches should respond more strongly (i.e. become vigilant, feed less, abandon feeder) to feeder predators than non-feeder predators. We observed goldfinches at two established feeders and used playbacks of two predator types (feeder predators = high risk and non-feeder predators c::: lower risk) and control species (non-predators) recordings to measure behavioral and vocal responses to auditory predator cues by counting the number of seeds consumed, the time a goldfinch spent vigilant, and whether or not a bird fled the feeder. We planned to measure fluctuations in number and type of calls (e.g., contact versus alarm calls), but no vocal responses were produced by the goldfinches during the trials. We found no difference in behavioral reactions to predator types, and our hypothesis that responses to predators would differ with threat level was not supported. However, vigilance increased significantly from control (unthreatening) species to predator species (F=0.27, p= 0.0008) which decreased seed consumption (F""l .4, p""0.25), indicating that vigilance is greatly increased when birds forage for food under predatory pressure. This trade-off is a major consequence of predation and is a driving force in organizing avian communities such as flocks.
Marsh, Kate, "Behavioral and Vocal Responses of the American Goldfinch (Carduelis Tristis) to Predatory Bird Calls" (2017). Senior Honors Theses & Projects. 545.