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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Wildlife & Fisheries Conservation

Year Degree Awarded

2018

Month Degree Awarded

May

First Advisor

David I. King

Subject Categories

Population Biology

Abstract

To better conserve threatened species, conservationists need to understand the processes that affect species during their entire life cycle, including ‘carry-over effects’ which can occur if individuals’ previous experience influences their current or future performance. We studied prairie warblers (Setophaga discolor) to examine carry-over effects in a Nearctic-Neotropical migratory bird. Using carbon isotopes in birds’ blood as a measure of habitat moisture, we first assessed the effects of rainfall and habitat on the condition of prairie warblers wintering in The Bahamas. Annual variation in rainfall and spatial moisture interacted to influence birds’ condition: during a winter with less rainfall, most birds lost mass and muscle, but more so for birds that occupied drier habitats. During a winter with more rainfall, most birds did not lose mass or muscle regardless of habitat use.

Using stable isotopes, we assessed if winter habitat use carried over to affect birds’ phenology and reproductive success in Massachusetts, USA. We did not find evidence of carry-over effects for second-year males or females, but our sample sizes were relatively small. In two of three years, our observations of after-second-year (ASY) males were consistent with our expectation that birds wintering in drier habitat would arrive later on the breeding grounds. We found no evidence for time-mediated constraints on reproductive performance for ASY males.

Using a winter rainfall index and carbon isotopes to indicate winter habitat moisture, we examined carry-over effects initiated during the breeding season. Juvenile birds that hatched earlier acquired wetter winter habitat during drier winters, and during all winters for male birds. Winter habitat acquired as a juvenile was used throughout the bird’s life. Hatching date can thus influence a bird’s lifetime winter habitat quality, which other studies found can influence birds’ survival and reproduction. Adult males that successfully reproduced in the previous breeding season obtained wetter, better-quality habitat in the subsequent winter season, indicating no apparent cost of caring for young on winter habitat acquisition. Overall, our novel results are important for better understanding the full annual cycle of migratory birds and how birds might be affected by climate change.

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