Are Seasonal Interactions Mediated by Stress Responses in a Short-Distance Migratory Bird?

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2021-05

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The Ohio State University

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Various stages within animals' annual cycle can affect one another and, thus, are not discrete events in time. What occurs during one period of the annual cycle (e.g. non-breeding) can alter the success or survival of animals in another period (e.g. breeding) of their annual cycle through non-lethal factors. These effects are termed “seasonal interactions” and are fueling a rapidly growing body of knowledge advancing our understanding of how populations are limited across the full annual cycle. In order to examine these seasonal interactions, this study aims to determine if they occur across nonbreeding stages in a short-distance migratory bird, the white-throated sparrow (Zonotrichia albicollis). These sparrows are quite abundant throughout the eastern U.S. and have well defined annual cycles. Nearly all studies examining seasonal interactions have focused on neotropical migrants and effects on the breeding season. I measured physiological stress during nonbreeding stages to determine if seasonal interactions exist between the stages of molt, wintering, and spring migration. I found that stress levels (measured by corticosterone in feathers) varied by stage and sex and higher stress in molt correlated with decreasing fat reserves during winter. However, higher stress in winter correlated with increasing fat reserves during winter, and later departure for spring migration. Thus, it appears stress hormones and fat interact in complex ways across the annual cycle. A complete grasp of the full annual cycle, and not just the breeding season, is critical for conservation as the world is experiencing a drastic decline in “common” migratory birds, like the white-throated sparrow.

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