Age-Specific Differences In Fat Reserves And Migratory Passage Of Setophaga Striata (Blackpoll Warbler)

Adequate fat reserves are vital for long non-stop transatlantic avian-migration movements, such as those made by Setophaga striata (Blackpoll Warbler). Over a 5-y period, we studied differences in preparedness (determined by presence of fat content and arrival time at stopover locations) between hatch-year (HY) and after hatch-year (AHY) Blackpoll Warblers at 3 stopover sites (Hancock and York counties in Maine, and Plymouth County in Massachusetts) covering 2.65° latitude along the Gulf of Maine. Migration timing varied across a latitudinal gradient and between age classes. In September, AHY Blackpoll Warblers were more abundant in the northern and central counties, but HY birds mostly passed through in October. Compared to AHY Blackpoll Warblers, our results suggest that HY birds migrated along a more northern route. After hatch-year birds had higher fat-content than HY birds at the northern and central sites. However, AHY birds had lower fat-content at the southernmost site. After hatch-year birds were more abundant than HY birds at the southern-most site. Overall, across our study region, our data illustrate that Blackpoll Warblers show age-related differences in fall-migration strategy; hatch-year birds may simply need more time at stopover sites to build up fat reserves prior to large-distance flights