Habitat preference facilitates successful early breeding in an open-cup nesting songbird

Selecting breeding habitats that ameliorate environmental limits on fitness and facilitate successful reproduction should benefit individual animals. This is particularly true in the temperate zone, where breeding early in a season presents a unique series of environmental challenges that can limit an individual's fitness. While many studies document links between habitat quality and reproductive success, few identify the cues used to assess habitat quality or the components of reproduction most influenced by occupying higher quality habitat, particularly during the early breeding season. We used detailed spatial maps and observations of all early season nesting attempts in an insular song sparrow (Melospiza melodia) population over 38 years to estimate the influence of nest-site preference on reproductive success and to test whether relative microclimate or food availability may act as cues for early season site selection. Female sparrows in preferred early season nest sites had earlie...