Foraging behavior and ecology drive the evolution of humeral shape in hummingbirds

Skeletal morphology is central to avian flight performance and ecological adaptation. In hummingbirds, the humerus is critical for power generation and wing control, yet its evolutionary diversification remains poorly understood. We integrate geometric morphometrics, phylogenetic comparative methods, and ecological data to study humeral shape evolution across a diverse sample of 80 hummingbird species. Humeral shape variation was associated with ecological and geographical variables, including body mass, foraging strategy, range size and latitude. Larger body mass or smaller humeri corresponded to more robust, curved shapes, consistent with biomechanical demands of supporting greater forces. In contrast, broader geographic ranges are associated with more slender shapes, possibly reflecting aerodynamic efficiency across variable environments. Humerus shape also changed with foraging strategy: traplining species, which visit flowers along dispersed routes, exhibit elongated humeri favoring efficient, sustained flight, whereas territorial species showed shorter, robust shapes suited to rapid maneuvers. Morphological evolution rates differed among strategies, with trapliners showing highest rates, and increased significantly with range size. Strong phenotypic integration within the humerus indicated that evolutionary changes are tightly coordinated across the bone regions. These findings demonstrate how ecological pressures, scaling effects, and developmental constraints together shape flight-related morphology, underscoring the adaptive flexibility of the avian skeleton.