Passerine migrant stopover duration and spatial behaviour at an urban stopover site

Migration routes of many Nearctic-Neotropical landbirds pass through the most urbanized regions of North America. Migrants are known to use urban habitats as stopover sites and often occur in cities at exceptional density; yet knowledge of migrant behaviour and ecology in such places is surprisingly limited. We radio-tracked ovenbirds (Seiurus aurocapillus) during stopovers in a New York City park to obtain some of the first detailed information on how landbird migrants utilize an urban habitat as a stopover site. We examined fine-scale movement patterns, home range sizes, stopover durations, and how arrival condition affected each of these metrics. During both seasons, most birds moved widely throughout the site upon presumed arrival and then either continued migration that night or settled into a more defined area on subsequent days. Area usage varied markedly among individuals during both seasons, ranging 1-16 ha. Stopover durations averaged 3.0 days (range = 1-10 days) during spring and 2.9 days (range = 1-14 days) during autumn. Spatial behaviours and stopover durations were not influenced by arrival condition during spring, and during autumn only movement rates and displacement distances were significantly (negatively) condition-related. Our findings do not support previous assumptions that urban stopover habitats are only used by migrants briefly in times of urgency when alternatives are unavailable. At least half of the birds we studied stopped over for multiple days during both seasons, and bird movements were indicative of an ability to search for, locate, and occupy suitable micro-sites. Ovenbird behaviour in our study site was similar in many ways to what has been observed in recent telemetry studies of ovenbirds and other passerine migrants at various non-urban stopover sites.