Mass Changes Of Migratory Landbirds During Stopovers In A New York City Park

Abstract

We measured rates of mass change of eight species of migratory passerines in a New York City park during three consecutive spring and autumn migrations to evaluate the quality of an urban habitat as a stopover site. We also examined seasonal differences in body condition. Linear regressions of a condition index on time of day detected significant hourly mass gain by Magnolia Warbler (Dendroica magnolia), Black-throated Blue Warbler (D. caerulescens), Ovenbird (Seiurus aurocapilla), and Northern Waterthrush (S. noveboracensis) during spring, and Common Yellowthroat (Geothlypis trichas) during autumn. Swainson's Thrush (Catharus ustulatus) showed significant mass loss during autumn. Significant spring mass gain rates ranged from 0.99 to 2.46% of mean body mass/hr. Common Yellowthroat gained 1.28% of mean body mass/hr during autumn. Most species were heavier and fatter in spring than autumn. The significant mass gain rates were comparable to those in similar studies in more pristine areas. Our results suggest the urban stopover site we examined is a place where migrants can sufficiently replenish energy stores. This highlights the importance of conserving and properly managing remaining green spaces in urban areas along major migratory bird flyways.