Crysler, Zoe L, Robert A Ronconi & Philip D Taylor. 2016. Differential fall migratory routes of adult and juvenile Ipswich Sparrows (Passerculus sandwichensis princeps). Movement Ecology, 4(3).
Summary (AGH): Migration and wintering can be the riskiest parts of a songbird’s life. Yet, despite our deep knowledge of many songbirds’ breeding habits, we know little about these phases because they’re so hard to study. Ipswich Sparrows are ideal for such research, because they breed only on Sable Island, yet winter along the long yet narrow strip of dunes along the east coast. Thus, there’s likely to be variation in how far individual birds have to travel, and how mild the winters they experience are. At the same time, however, thanks to the narrowness of their winter range, they are relatively easier to find than most other songbird species, which winter across wider ranges. This study explores the challenge that birds face when leaving Sable Island for the risky cross-water flight to the mainland in fall. Using small, backpack-carried tags that transmit individually distinct radio signals, which VHF receiving towers placed along the migration route can detect, the study showed that adult and young-of-the-year Ipswich Sparrows leave the island in different ways. Juveniles leave nearly a month before adults on average, and take shorter water crossings, landing first in mainland Nova Scotia, then crossing the Bay of Fundy before continuing on. Adults, in contrast, fly more directly to the wintering grounds in the eastern US. Juveniles might be trading off less risky flights against longer time spent migrating.