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

<b>Abstract</b><br/>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 earlier laying dates, exhibited more energetically efficient incubation behaviour and produced more offspring that recruited to the population than those nesting in less-preferred sites. Preference for potential nesting sites was positively related to leaf damage by Lepidopteran larvae, an indicator of food abundance, negatively related to early season microclimate, likely due to greater vegetation cover, and unrelated to site-specific plant phenology. Our findings show that breeding in preferred, high-quality habitat may offer females a fitness advantage by facilitating early laying and the production of offspring more likely to recruit to the population at a lower potential reproductive cost to the parent. We provide a clear demonstration of potential links between habitat preference and quality and their contributions to the ecology and life history of animals in seasonal environments.