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https://hdl.handle.net/2142/87842
Description
Title
Habitat Selection by Yellow -Headed Blackbirds
Author(s)
Ward, Michael Patrick
Issue Date
2004
Doctoral Committee Chair(s)
David Enstrom
Department of Study
Animal Biology
Discipline
Animal Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Zoology
Language
eng
Abstract
Migratory birds have the ability to select a breeding site from a large number of sites across a large geographic area. Therefore, one might expect that migratory birds would select the site where they would realize the greatest fitness. However, little is known about how and why migratory birds select breeding sites. I investigated habitat selection at various spatial scales in a neotropical migrant, the Yellow-headed Blackbirds (Xanthocephalus xanthocephalus). This research was conducted in two declining populations in northeastern Illinois. I found that at the largest spatial scale, immigrants appear not to settle in the Illinois populations, probably because of their location on the periphery of the species' range. However, once in the population, individuals realize high reproductive success, and use the cue most predictive of future reproductive success to determine where to breed. Dispersing individuals use conspecific reproductive success, the number of young per hectare to determine the site at which to breed. Both males and females assess conspecific reproductive success the year prior to breeding at a site. I found that individuals that were going to disperse visited potential breeding sites late in the breeding season, suggesting they were evaluating the quality of the potential breeding sites. I also investigated how individuals in two populations determined whether to return to former breeding sites and why the degree of site fidelity in these populations differed. The degree of site fidelity appears to differ due to differences in population density. In the denser population, fewer individuals dispersed, while individuals in the lower density population were more likely to disperse. I propose that density affects the cost of dispersal, and therefore the rate of site fidelity. Different factors also influence site fidelity. In the low-density population, individuals used conspecific reproductive success, while in the high-density population individuals used their own reproductive success. This research demonstrates how understanding habitat selection at various spatial scales is necessary to understand the population dynamics of a species.
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