Due to the overlap of the Atlantic Flyway with some of the most urbanized regions of North America, the habitats remaining within cities may play an important role in bird migration. Yet, the use of urban parks by migrating birds is currently poorly understood. To determine if an urban habitat is serving as a suitable stopover site, I investigated the energetics of 8 species of migratory songbirds in Bronx Park (Bronx, NY) during two consecutive spring and fall migrations. Fat score, body mass, and rate of mass gain of birds of different ages and sexes were compared within and between migration seasons. For comparison to other studies, I calculated possible flight ranges. Fat score and condition index was significantly higher in spring for most species. There were few significant sexual differences in fat score or condition index in spring and few significant age-related differences in fall. Rate of mass change was positive in 12 of 17 possible combinations of species and season. Rates of mass gain were greater in spring than fall for most species. Flight ranges were comparable to those calculated in studies in rural areas and suggest most migrants in Bronx Park store enough energy to fly longer distances than are possible in the course of one night at the assumed average flight speed of small passerines. High fat scores, condition indices, and flight ranges, and positive rates of mass gain demonstrate the study site is a place where migrants can sufficiently restore depleted energy reserves. These findings highlight the importance of conserving and properly managing the remaining green spaces in urban areas situated along migratory bird flyways.
Project Report: The Energetics and Stopover Ecology of Neotropical Migrant Passerines in an Urban Park