Abstract:
Long-distance migration is characterized by periods of flight, when energy stores are consumed, and periods of stopover, when energy stores are replenished. The duration of the migratory period is largely determined by time spent at stopover sites. The time constraints imposed on spring migrants should act to minimize the time spent on migration, yet spring migrants often remain at stopover sites for extended periods. We measured the influence of arrival fuel stores, arrival date, and foraging movement rate on the duration of Red-eyed Vireos (Vireo olivaceus) that remained at stopover sites for more than 1 day. We captured spring migrants in mist-nets as they arrived after crossing the Gulf of Mexico. We released them at an inland site and continuously followed (radio-tracked) their movements until departure. Departure time was confirmed with extensive ground searches and aerial surveys. Migrants remained at the stopover sites from 1 to 8 days (2.80 ± 0.14 days). Less than one-third of migrants were transient, leaving the night following release (32 %). Of the migrants that remained more than 1 day, those that arrived with low fuel stores remained longer than those that arrived with more fuel stores. Only migrants arriving early in the spring stayed for extended periods of time (>5 days). Further, migrants that moved faster within the stopover landscape presumably replenished fuel stores faster because they did not remain as long as migrants that did not move as quickly. When arrival fuel stores, arrival day, and departure day were known, we found multiple factors influenced the length of stay at spring stopover sites. Early spring migrants with low fuel stores that moved slowly through the landscape spent the most time at spring stopover sites.
