Doctor of Philosophy
Migration routes of many Nearctic-Neotropical landbirds pass through the most urbanized regions of North America. Migrants use urban habitat fragments as stopover sites and commonly occur in cities at exceptional density. Yet, knowledge of migrant stopover biology and refueling opportunities in such places is severely limited. This dissertation examined several aspects of migrant stopover biology in the New York metropolitan area to gain a more holistic understanding of how migratory landbirds utilize urban stopover sites, and ultimately to assess the quality of urban habitats as stopover sites. I first generated morphometric predictive models using salvaged bird specimens to allow me in subsequent studies to noninvasively measure the energetic condition (fat mass) of migrants in New York City (NYC). Next I compared the refueling performance of migrants in NYC to that of conspecifics in less-disturbed forests outside of the city. Blood plasma metabolite profiles indicated that refueling conditions for migrants were no poorer in NYC than in the non-urban habitats. Further, migrant refueling rates were comparable to, and in some cases higher than, those reported in the literature for birds at various non-urban stopover sites. Measures of arthropod biomass suggested food abundance for insectivorous migrants was also similar within and outside NYC. I then showed that stopover refueling in NYC often involved substantial increases in lean mass. This finding carries implications for stopover habitat management practices, as migrants using these sites will require high-protein foods in addition to the lipid- and carbohydrate-rich foods that maximize fattening rates. Next, radio-telemetry data from a small pilot study provided one of the first descriptions of migrant stopover durations within a city. Stopover durations ranged 1-14 days and were negatively related to fat mass, but not lean body mass, upon arrival. A larger-scale telemetry study revealed that migrant spatial behaviour in NYC was in many ways similar to what has been observed in passerine migrants in non-urban areas. Movement patterns were indicative of an ability to search for, locate, and occupy suitable microhabitat, and temporary home ranges suggested forest size was more than sufficient to meet their area requirements. Collectively, these studies provide a comprehensive assessment of the quality of urban habitats as migratory bird stopover sites. Findings indicated that the sites examined are functioning in the same fashion as less-disturbed, larger forest tracts elsewhere. No evidence was found to suggest that stopover refueling conditions within one of the world’s most urbanized landscapes are inadequate for migrating landbirds.
Seewagen, Chad L., "Stopover biology of migratory landbirds in a heavily urbanized landscape, the New York metropolitan area" (2010). Electronic Thesis and Dissertation Repository. 31.