Data from: The relationship between female brooding and male nestling provisioning: does climate underlie geographic variation in sex roles?

Comparative studies of populations occupying different environments can provide insights into the ecological conditions affecting differences in parental strategies, including the relative contributions of males and females. Male and female parental strategies reflect the interplay between ecological conditions, the contributions of the social mate, and the needs of offspring. Climate is expected to underlie geographic variation in incubation and brooding behavior, and can thereby affect both the absolute and relative contributions of each sex to other aspects of parental care such as offspring provisioning. However, geographic variation in brooding behavior has received much less attention than variation in incubation attentiveness or provisioning rates. We compared parental behavior during the nestling period in populations of orange-crowned warblers (Oreothlypis celata) near the northern (64°N) and southern (33°N) boundaries of the breeding range. In Alaska, we found that males were responsible for the majority of food delivery whereas the sexes contributed equally to provisioning in California. Higher male provisioning in Alaska appeared to facilitate a higher proportion of time females spent brooding the nestlings. Surprisingly, differences in brooding between populations could not be explained by variation in ambient temperature, which was similar between populations during the nestling period. While these results represent a single population contrast, they suggest additional hypotheses for the ecological correlates and evolutionary drivers of geographic variation in brooding behavior, and the factors that shape the contributions of each sex.

对栖息于不同环境的种群开展比较研究，可揭示影响双亲抚育策略差异的生态条件，其中包括雌雄两性的相对投入比例。雌雄双亲的抚育策略，实则为生态条件、配偶贡献与子代需求三者间相互作用的体现。气候被认为是驱动孵卵与育雏行为地理变异的核心因素，并可由此影响两性在子代投喂等其他抚育环节中的绝对投入与相对贡献。然而相较于孵卵专注度或投喂频率的变异，育雏行为的地理差异迄今尚未受到足够关注。本研究针对繁殖分布区北部（北纬64°）与南部（北纬33°）的橙顶虫森莺（*Oreothlypis celata*）种群，比较了二者在雏鸟期的双亲行为。在阿拉斯加种群中，雄性承担了绝大多数的食物投喂任务；而在加利福尼亚种群中，两性的投喂贡献则基本持平。阿拉斯加种群中更高的雄性投喂投入，似乎让雌性能够将更多时间用于暖育雏鸟。令人意外的是，种群间的育雏行为差异无法用环境温度变异来解释——雏鸟期两地的环境温度并无显著差异。尽管本研究仅针对一对种群开展对比，但研究结果为探索育雏行为地理变异的生态关联与进化驱动因素，以及塑造两性抚育贡献的各类因子提供了新的研究假说。