Revealing migratory path, important stopovers and non-breeding areas of a boreal songbird in steep decline

Abstract

The Olive-sided Flycatcher (Contopus cooperi) is a steeply declining aerial insectivore with one of the longest migrations of any North American passerine. We deployed light-level geolocators and archival GPS tags on breeders in boreal Alaska to determine migratory routes, important stopovers and non-breeding locations. Data from 16 individuals revealed a median 23,555 km annual journey (range: 19,387, 27,292 km) over 95 days (range: 83, 139 days) with wintering occurring in three regions of South America (NW Colombia/Ecuador, central Peru and W Brazil/S Peru). We developed a new method to identify “Important Stopovers” by quantifying intensity of use (a function of bird numbers and stop durations) along migratory routes. We identified 13 Important Stopovers that accounted for ~66% of the annual migratory period, suggestive of refueling activities. Some sites coincided with key areas previously identified for other Neotropi- cal-Nearctic migrants. Percent land “protected” at Impor- tant Stopovers, as defined by IUCN, ranged from 3.8% to 49.3% (mean [95% CI]: 17.3% [9.6, 25.0]). Total migration speed did not differ by season (median: 255 km day-1, range: 182, 295km day-1), despite greater spring travel dis- tances. Birds with longer non-breeding periods, however, migrated north faster. Climate-driven mismatches in migratory timing may be less of a concern for western than for eastern flycatcher populations, given recent con- generic analyses (C. sordidulus, C. virens). However, accel- erated high-latitude changes, may nonetheless impact boreal breeders.