Reproductive consequences of migration decisions by Ipswich Sparrows (Passerculus sandwichensis princeps)

The costs and benefits associated with migration differ depending on individual decisions regarding the distance to migrate and where to winter. These decisions affect an individual's winter experience, which may in turn impact reproductive success the following breeding season. We investigated whether winter location influences performance on the breeding grounds in a short-distance migrant, the Ipswich Sparrow (Passerculus sandwichensis princeps Maynard, 1872), endemic to Sable Island, Nova Scotia, Canada. We used stable hydrogen isotope analysis to infer the winter location of individuals breeding on Sable Island, and investigated whether body condition, timing of breeding initiation, and number and condition of nestlings varied with winter location. Males wintered farther north than females, and males from the northern end of the wintering range were in better condition, established territories earlier, and tended to produce heavier nestlings than those wintering farther south. Conversely, females that wintered farther south had significantly earlier first egg dates than those that wintered farther north. The results of this study suggest that individual decisions about migration distance can impact reproductive success and that optimal winter locations differ between male and female Ipswich Sparrows.