Abstract
BackgroundIsland breeding birds present an ideal system for studying migratory movements in passerines because their populations are clearly demarcated, and individuals must depart on migration from a single location. The Ipswich Sparrow (Paserculus sandwichensis princeps) is a subspecies of the Savannah Sparrow that breeds exclusively on Sable Island, Nova Scotia, Canada and winters along the Atlantic coast of North America. We used a network of 34 automated VHF telemetry receivers to track radio-tagged adult and juvenile Ipswich Sparrows from their breeding island southward through the first half of their fall migratory journey.ResultsWe compared adult to juvenile timing and routes. We show that juveniles leave the island approximately 24 days prior to adults and remain temporally separated from them during migration through Nova Scotia. Juveniles have different overwater orientations that result in migratory routes with shorter ocean crossings and a longer overall distance travelled compared to adults. Juveniles also have more frequent and longer stopovers, and displayed some reverse migration.ConclusionWe demonstrate that migratory routes differ between adults and juveniles, suggesting that routes change as individuals age, possibly through learning or social interactions. These differential routes also suggest that sparrows experience risk in different ways with juveniles selecting shorter overwater flights with less navigational risk at the cost of increased time spent in migration.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-016-0067-8) contains supplementary material, which is available to authorized users.
Highlights
Island breeding birds present an ideal system for studying migratory movements in passerines because their populations are clearly demarcated, and individuals must depart on migration from a single location
Ipswich Sparrows remained on Sable Island for 31–86 days after tagging
All individuals detected on the mainland were initially detected in Nova Scotia (Table 2); 29 of these (4 adults, 25 juveniles) were subsequently detected in coastal areas of the Gulf of Maine
Summary
Island breeding birds present an ideal system for studying migratory movements in passerines because their populations are clearly demarcated, and individuals must depart on migration from a single location. Juveniles may be less able to avoid predators [9] and orientate in appropriate directions [10], have more variability in their orientation [11], and take longer and more frequent stopovers [12, 13]. Both adults and juveniles are known to undertake flights in inappropriate migratory directions in both spring and fall [14,15,16]. Such ‘reverse migrations’ and ‘landscapescale stopover movements’ may be due to orientation errors, overshooting targets, or for gathering information about the environment [17, 18]
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