Geometric morphometric analysis of the humerus in New and Old World vultures

The vulture guild is composed of two distinct groups, Old and New World, which provide a unique insight into how morphology varies among convergent species. All vultures are considered to be large birds of prey that utilize a style of flight called thermal soaring to search and feed primarily on carrion. Even though this flight style is exhibited among all 23 species, slight variations in their skeletal morphology may relate to their differences in ecology. We hypothesized that vulture humeral morphology varies in relation to these organisms' habitat, average body mass, courtship displays, and migratory behavior. To address this hypothesis, we used three-dimensional geometric morphometrics to measure the overall shape differences of vulture humeri. Humeral morphology was found to vary most by habitat association and migratory tendency. The humeri of vultures that inhabit forested areas exhibit features that suggest increased flapping flight compared to those in open and mountainous regions. Migratory species were found to possess more robust features near the glenohumeral joint. We found these (and other features) have some utility for predicting ecology and behavior, but we suggest that further investigation into skeletal and muscular wing elements may reveal greater understanding of the habits of extinct vulture species.