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The importance of linking periods of the annual cycle for understanding life-history tradeoffs in a migratory songbird

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Title: The importance of linking periods of the annual cycle for understanding life-history tradeoffs in a migratory songbird
Author: Mitchell, Greg
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Norris, RyanGuglielmo, Chris
Abstract: In migratory vertebrates, the optimal timing of successive life history stages is relatively inflexible. As a result, life history trade-offs that occur during breeding may influence individual success in subsequent stages because there is little time to mitigate negative costs that are incurred, or because the onset of subsequent stages is delayed. In migratory songbirds, understanding how breeding events carry over to influence individual success has been challenging because individuals are difficult to track once breeding is complete. I studied an island breeding population of migratory Savannah sparrows (Passerculus sandwichensis) and tracked individuals from breeding up until the onset of autumn migration. In Chapter 1, I investigated the effects of early life events on body condition during the pre-migratory period and first year apparent survival. I found that juveniles fledging from larger broods were in poorer condition at fledging, had lower fat stores prior to migration, and had lower first year apparent survival. In Chapter 2, I examined the effects of life history trade-offs made by adults during breeding on pre-migratory body condition and annual apparent survival. I did not find evidence for a trade-off between reproductive effort or date of breeding completion with annual apparent survival or body condition during the pre-migratory period, but instead found that adults with the highest reproductive effort and later dates of breeding completion were more likely to survive until the following year. In Chapter 3, I examined the effect of timing of breeding completion and fledging on the date of fall migration. I found that both variables had strong positive effects on date of departure. Together, my results suggest that successful migration in juveniles is influenced by early life events, but that any potential costs incurred by adults during the breeding season likely has little influence on survival during migration.
Date: 2011-09
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