Habitat-specific demography of a long-distance, neotropical migrant bird, the Eastern Kingbird

I used data from a 10-yr study of Eastern Kingbirds (Tyrannus tyrannus) bre eding in three habitats in the Charlotte Valley of central New York to desc ribe population trends, and to examine how population dynamics varied with habitat-specific estimates of reproductive output, adult dispersal, and sur vival. Although breeding date was slightly earlier on the floodplain than t he upland. my other comparisons showed that clutch size, egg mass, or the n umber of young lost to starvation or predators did not vary with habitat. H owever, floodplain pairs had the lowest annual productivity because signifi cantly more of their eggs were eaten by predators during incubation. Males tended to exhibit higher survival and site fidelity than females, but in bo th sexes, survival was highest on the floodplain and lowest in the upland. Most dispersing individuals of both sexes moved toward the creek (significa nt in males). As a result of this and the moderately high survival of adult s that bred along the creek, the creek population remained stable between 1 989 and 1998. whereas the floodplain. upland, and total population tended t o decline (2.5%/yr). Counts of kingbirds from Breeding Bird Surveys (1989-1 996) conducted within 100 km of the study site also showed significant decl ines. 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 sur vival during the latter half of the study. Calculation of habitat specific population growth rates suggested that all three habitats, and thus the ent ire Charlotte Valley system, was a population sink whose numbers were suppl emented substantially by outside immigration. However, productivity along t he creek (and upland) was density dependent, suggesting also that the creek may function as a "pseudosink." My results suggest that spatial and tempor al (i.e., successional) changes in habitat quality may have led to increase d permanent emigration of adults, and declines in population size. The impo rtance of outside immigration also suggests that population dynamics can on ly be understood by evaluating local trends within a larger geographic cont ext.