Diversity in the shapes of avian eggs has intrigued biologists for centuries, and recent studies at a range of taxonomic scales suggest that egg shape can be a powerful lens through which to view morphological adaptation. At a broad taxonomic level, we previously examined egg shape in 1400 species (Stoddard et al. 2017). Our study, which contained a detailed analysis of the egg shape morphospace and a new biophysical model of egg shape formation, included a broad-scale phylogenetic comparative analysis of egg shape across more than 1200 species representing 34 orders and 143 families. We found that, at this global scale, most variation in egg shape is correlated with phylogenetic history, an adult bird’s body mass and egg size. We also found a significant correlation between egg shape and hand-wing index, a measure of wing shape that provides a general estimate of flight ability, prompting us to consider the possibility that adaptations for flight might be important drivers of egg shape variation.