Evidence for frequency-dependent selection in House Wrens, but not Eastern Bluebirds

Abstract

Frequency-dependent selection occurs when predators alter their prey choice to target abundant prey. We tested whether two species of insectivorous songbirds exhibited similar frequency-dependent selection behavior. House Wren (Troglodytes aedon) and Eastern Bluebird (Sialia sialis) routinely occupy nest boxes established over 700 acres at Missouri Western State University. During the 2018 breeding season from April through July, House Wrens consumed more sentinel prey from the color station that had previously appeared in higher frequency after four days of training. Eastern Bluebirds did not consume more of the previously abundant prey color stations and neither species showed a preference when the abundant color was reversed for the second half of the experiment which may be explained by latency in switching previously learned behaviors. Consequently, House Wrens demonstrated an initial frequency-dependent foraging strategy, but the Eastern Bluebirds did not. These results indicate how generalist insectivores that nest in the same habitat differ in their foraging strategies and behaviors.