For six months of each year, Neotropical forests host the highest known diversity and density of wintering migrants. Habitat loss and conversion of more than 3.5 million ha of Neotropical forests a year is frequently linked to declines in Neotropical migrants, however, data on habitat use in the wintering grounds is very limited. In this thesis, I examine habitat use, across three land cover types for wintering Yellow Warblers (Setophaga petechia) and show that in the lowlands of Jalisco, Mexico, seasonal agriculture with hedgerows, provides high quality winter sites. Yellow Warbler originating from Western Canada, were found in the highest densities in agricultural habitats, intermediate in riparian forests and lowest in coastal scrub-mangrove. Birds wintering in agriculture and riparian forest had higher apparent monthly survival compared to birds in scrub-mangrove and were able to regrow higher quality replacement tail feathers. However, I found no evidence that traits linked to competitive ability (age, sex, or size) influenced the distribution of birds across different land covers. Together, these results demonstrate that current agricultural practices in western Mexico are unlikely to have contributed to the decline of Yellow Warbler populations in Canada. Overwintering in agriculture did not appear to negatively impact the Neotropical migrant community in western Mexico. Neotropical migrants were more abundant in agriculture, and had similar species diversity and beta-diversity to riparian forests. In contrast, although a few resident species were frequently found in agriculture, resident species had lower species diversity in agriculture compared to riparian forest community. Collectively these results demonstrate that individual species, and particularly the Neotropical bird community can utilize human altered landscapes on the wintering grounds in Mexico. However, native habitats are key to retaining the full resident bird community. Identifying the features and spatial configuration of the working land that supports bird populations will be critical for the management and conservation of resident and overwintering birds.
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Thesis advisor: Green, David
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