Dale, C.A. 2008. Links between the winter and breeding seasons in a short-distance migrant, the Ipswich Sparrow (Passerculus sandwichensis princeps). MSc Dissertation, Dalhousie University.

Summary
Many North American birds winter in areas 1000s of miles away from their temperate breeding grounds. There is a growing body of evidence suggesting that winter events and location may affect some aspects of reproductive success in migratory birds. In this study, Catherine Dale investigated the effects of 1) a winter event (prealternate moult, i.e. partial winter moult), and 2) winter location, on breeding success in a short-distance migrant, the Ipswich Sparrow (Passerculus sandwichensis princeps). The Ipswich Sparrow, a subspecies of Savannah Sparrow (Passerculus sandwichensis), breeds almost exclusively on Sable Island, and winters in outer dunes along the Atlantic coast from Nova Scotia to Florida. Hydrogen stable isotope analysis was used to determine wintering latitude, and carbon and nitrogen stable isotope analysis was used to infer aspects of winter diet.
1) Prealternate moult only occurred in 25% of Ipswich Sparrows and was mainly restricted to tertials, rectrices and back feathers. There was no relationship between the incidence of prealternate moult and reproductive success, nor was prealternate moult related to winter location. The results suggest that prealternate moult is a relatively low-cost activity for Ipswich Sparrows, and that it may function to replace plumage degraded by sunlight.
2) Winter location affected reproductive success in both sexes. Males that wintered in the northern part of the wintering range established breeding territories on Sable earlier and were in better condition than those that wintered in the southern part of the wintering range. Northern-wintering males also tended to produce heavier nestlings than those wintering further south. Conversely, females that wintered towards the southern part of the wintering range had earlier first egg dates than those wintering further north. Individuals wintering further south relied mainly on a diet of C4 plants, while those wintering further north incorporated C3 plants in their diet. Nitrogen isotope ratios were not useful in determining trophic level, but were related to condition and therefore may provide information regarding quality of winter habitat.