Risk assessment during nest defense against three simulated predators by female northern house wrens (Troglodytes aedon)

Abstract

Offspring predation is one of the greatest obstacles to an organism's reproductive success, but parents vary in the strength of their response to potential predators. One explanation for this variable investment is that defending current offspring has the potential to lower future reproductive success if the predator is also capable of injuring or killing the parent. House wrens (Troglodytes aedon aedon) are cavity-nesting songbirds that defend against multiple species of nest predators including small mammals, birds of prey, and snakes. Here, we used three different predator decoys: two nest predators - an eastern chipmunk (Tamias striatus) and an eastern ratsnake (Pantherophis alleghaniensis) - as well as a predator of both offspring and adults - a juvenile Cooper's hawk (Accipiter cooperi) - to elicit nest defense and test whether females use risk assessment to modulate their antipredator behavior. We found that antipredator behaviors were not significantly different between the two nest predators, which posed a high risk to the nestlings, but lower risk to the parents as neither species frequently captures adult wrens. Females also did not differ significantly in their responses to the snake between years, suggesting that the population-level response might be consistent through time. However, female wrens never dove at or attacked the Cooper's hawk despite frequently attacking both the snake and chipmunk decoys. Collectively, these results show that female house wrens exhibit plasticity in their antipredator behavior, and they respond to different types of predators in a way that could maximize lifetime fitness while risking the loss of their current offspring.