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Article
Habitat-Specific Demography of a Long-Distance, Neotropical Migrant Bird, the Eastern Kingbird
Ecology (2001)
  • Michael T. Murphy, Portland State University
Abstract
I used data from a 10-yr study of Eastern Kingbirds (Tyrannus tyrannus) breeding in three habitats in the Charlotte Valley of central New York to describe population trends, and to examine how population dynamics varied with habitat-specific estimates of reproductive output, adult dispersal, and survival. Although breeding date was slightly earlier on the floodplain than the upland, my other comparisons showed that clutch size, egg mass, or the number of young lost to starvation or predators did not vary with habitat. However, floodplain pairs had the lowest annual productivity because significantly more of their eggs were eaten by predators during incubation. Males tended to exhibit higher survival and site fidelity than females, but in both sexes, survival was highest on the floodplain and lowest in the upland. Most dispersing individuals of both sexes moved toward the creek (significant in males). As a result of this and the moderately high survival of adults that bred along the creek, the creek population remained stable between 1989 and 1998, whereas the floodplain, upland, and total population tended to decline (2.5%/yr). Counts of kingbirds from Breeding Bird Surveys (1989–1996) conducted within 100 km of the study site also showed significant declines. Population size within the Charlotte Valley was positively associated with local adult male survival and seasonal productivity, and the declines in population size seemed to be linked most strongly to a drop in male survival during the latter half of the study. Calculation of habitat-specific population growth rates suggested that all three habitats, and thus the entire Charlotte Valley system, was a population sink whose numbers were supplemented substantially by outside immigration. However, productivity along the creek (and upland) was density dependent, suggesting also that the creek may function as a “pseudosink.” My results suggest that spatial and temporal (i.e., successional) changes in habitat quality may have led to increased permanent emigration of adults, and declines in population size. The importance of outside immigration also suggests that population dynamics can only be understood by evaluating local trends within a larger geographic context
Keywords
  • Bird populations--United States,
  • Avian biology,
  • Eastern Kingbirds
Disciplines
Publication Date
May, 2001
Publisher Statement
Copyright (2001) Ecological Society of America
Citation Information
Michael T. Murphy. "Habitat-Specific Demography of a Long-Distance, Neotropical Migrant Bird, the Eastern Kingbird" Ecology Vol. 82 Iss. 5 (2001)
Available at: http://works.bepress.com/michael_murphy1/32/