Redstart Stress Response Differs by Habitat
The American redstart, a small songbird that nests in North America and winters in the tropics, gets stressed out just like the rest of us. But does the stress response have any long-term consequences?
Scientists studied redstarts on their wintering grounds in Jamaica to find out. Scientists captured the birds, held them for half an hour (enough time for the stress response to kick in) and took a blood sample.
Researchers analyzed the blood samples for corticosteroids, a hormone that is elevated when the stress response is high. It was thought that birds with a healthy stress response would be birds that would be more likely to survive—think of the "fight or flight" response.
The redstarts were marked with a uniquely-numbered metal leg band and recaptured in subsequent years. Comparing how long the birds lived with their stress response would give clues as to the role stress plays in a bird's life.
Data analysis showed that birds that wintered in scrubby habitats, and had high-stress responses (high corticosteroid levels), were more likely to return in later years. Interestingly, birds that wintered in mangrove habitats did not show this pattern; high-stress levels were not found in returning birds.
Why the discrepancy? Mangroves are a better habitat for redstarts to overwinter in than scrub. Mangrove habitats offer more food and water, so the birds maintain their weight better throughout the winter, and can leave earlier on spring migration, get better breeding habitats, and raise more young.
Mangroves, therefore, appear to be pretty easy on the stress levels. Scrub, on the other hand, is a high-stress environment. Birds that have a high-stress response appear to do better in a high-stress environment.
This article summarizes the information in this scientific paper:
Angelier, Frederic, Holberton, R. L. and Marra, Peter P. 2009. Does Stress Response Predict Return Rate in a Migratory Bird Species? A Study of American Redstarts and their Non-Breeding Habitat. Proceedings of the Royal Society (London) B, 276(1672): 3545-3551.
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