An 18-year study of migration and stopover ecology of Tennessee warblers in Kalamazoo County, Michigan

Nearctic-neotropical passerines may spend up to one-third of the year in migration. Stopover sites have a critical role in providing migrant passerines with areas to rest and replenish fat stores. We characterized the stopover ecology of the Tennessee Warbler (Oreothlypis peregrina) at an inland site in Vicksburg, Michigan, using data from 4,607 warblers captured between 1990 and 2007. The recapture rate ranged from 1.6 to 12.1% annually and recaptured migrants averaged small but significant mass gains. Estimates of mass change using regression of mass on time of capture also suggested mass increases at this site. Recapture rate and mass gain estimated by regression varied significantly across the 18 years of study, although stopover length and mass change among recaptured individuals did not. Adult (after hatching year, AHY) warblers in active flight feather molt had an average lower mass and were four times more likely to be recaptured than non-molting adults. Over 95% of birds captured were hatching year (HY). The average condition and mass gains estimated by regression of HY warblers were lower than that of AHYs, but recapture rate, stopover length, and mass gains by recaptured individuals did not differ between the two age groups. The high number of captures and mass gains demonstrate the value of this site for fall migrant Tennessee Warblers. The annual differences in recapture rate and mass gains reported in this study suggest that several years of data may be needed to develop an accurate assessment of the typical use of a stopover site by migrants. Key words: age-related migration, annual variation, fall migration, inland stopover, mass change, molt, Oreothlypis peregrina.
Nearctic-neotropical migrants spend up to a third of each year migrating, using stopover sites to rest and/or replenish their fat stores along the way (Mehlman et al. 2005). Migrants are [...]