DISSERTATION RESEARCH: Survival and performance costs of phenotypic responses to predation risk

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This study investigates whether young songbirds that grow faster and leave the nest earlier because of a higher risk of nest predation have lower survival rates after leaving the nest. Predation can be a major source of mortality in wild animal populations. When the risk of predation is variable, prey species are expected to show flexible developmental responses that reduce their risk of being killed by predators. For example, young birds may grow faster and leave the nest earlier when nest predation risk is high. However, flexible developmental responses at early life stages may be physiologically costly and increase mortality at later life stages. By simulating increased predation, the researchers will experimentally determine the effects of variable nest predation on nestling growth rate and timing of fledging for Dark-eyed Juncos. Each bird will be tagged with a radio transmitter to determine their fates after leaving the nest. The study will also address whether activity levels and behaviors of fledglings reduce mortality risks and compensate for physiological costs. Results will provide critical insights on the key factors that control the growth and decline of wild animal populations, and lead to more effective management of these populations. In addition, the project will involve mentoring of both undergraduate and graduate students, and will develop educational materials for high school students. Educational videos for school age children will also be created for a local science education center.This project tests the hypothesis that faster growth of Dark-eyed Juncos in response to nest predation risk compromises mobility and causes increased mortality risk at older life history stages. Researchers will use speakers to broadcast sounds of typical nest predators to increase the perception of nest predation risk by parents and offspring to examine its consequences for mortality after fledging. Preliminary data show that young nestlings in 'high risk' nests leave the nest with shorter wings and are less adept at flying, but it is unclear if these same individuals are predated more often after leaving. Just before the nestlings leave the nest the researchers will attach radio transmitters to aid in tracking. Data will be collected on how often and how far the young birds move around each day after they leave the nest; whether they hide more often in denser vegetation where predators, like hawks, have greater difficulty getting to them; and whether they actually are more likely to die. Results will advance our understanding of carryover effects from growth plasticity on offspring mortality during later life stages.