Increased perception of predation risk to adults and offspring alters avian reproductive strategy and performance

Predation risk can inflict profound effects on prey by influencing prey behavior and other traits. Prey are often subjected to a diversity of predators, which can exert differential predation pressures on prey life-history strategies. In birds, breeding adults and offspring (as eggs, nestlings, and fledglings) are susceptible to different types of predators, and life-history theory predicts that breeding birds can adjust to adult versus offspring predation risk differentially via allocation of breeding investment. Here, we experimentally tested for the effects of perceived adult versus offspring predation risk on breeding birds' reproductive strategy and performance. On study plots with nest boxes used by the cavity-nesting Eastern bluebird Sialia sialis, we manipulated vocal cues of 3 avian predators that preferentially prey on either bluebird adults, or offspring, or both. We found that 1) increased perception of predation risk by all predator treatments reduced bluebird parental investment in egg production and/or post-egg nesting performance, and 2) increased perception of adult and offspring predation risks affected bluebirds differentially, with bluebirds exhibiting shorter nestling rearing periods under offspring, but not adult, predation risk. Our results provide experimental evidence for the nonconsumptive effects of predation risk on avian breeding behavior that can influence demographic vital rates and highlight the mechanisms by which breeding birds can adjust reproductive strategies under different predation risk situations.