Abstract

Sex ratios in bird broods can vary with environmental conditions and social structure; nestling sex ratios can influence adult population dynamics. In our Ithaca, NY population of American crow (Corvus brachyrhynchos), a cooperative breeder with males larger than females, nestling sex ratios are typically 50:50, but this may not be true in broods that have been reduced after hatching. In this study, we investigate whether there is a correlation between sex ratio and weather, and whether sex ratios differ between large healthy broods and small broods where nestlings have died before fledging. We predict that harsh weather (e.g., cold and rainy), will lead to small broods and skewed sex ratios due to the differential survival of the sexes. The direction of bias will suggest whether male competitiveness for food or the lower food needs of smaller females are more important.