Wing morphology and foraging ecology of Pacific Boobies: ecomorphology and character displacement

Wing and beak morphology are key components of the functional design of birds, and therefore an important determinant of their foraging ecology. This is especially the case for seabirds that traverse great distances in search of prey. Wing size and shape, expressed as wing loading and aspect ratio respectively, are parameters that can unveil differences and help understand the ecology of seabirds. Six species of boobies inhabit the Pacific, and five of them are the focus of this study: three pelagic species, the Masked (Sula dactylatra), Red-footed (S. sula), Brown (S. leucogaster), and two coastal species, Blue-footed (S. nebouxii) and Peruvian (S. variegata) Booby. They differ in their distribution (coastal vs. pelagic) and degree of overlap (sympatric vs. allopatric), and therefore were predicted to manifest differences in their wing and beak morphologies. Two of the most abundant species of seabirds along the South American coast are the Peruvian and the Blue-footed Booby. Although these species are largely allopatric, they overlap in northern Peru. Sympatric species exploit similar resources and consequently competition is likely to arise between them, resulting in the potential for character displacement in their sympatric range. Therefore, these two species would be predicted to exploit slightly different niches and foraging strategies that would be manifested in wing and beak morphology. The pelagic boobies showed ecological segregation among species and they differed in wing morphology from the two coastal boobies. Coastal boobies, on the other hand, showed evidence of character displacement in their wing morphology and body size, which suggests that competition plays an important role in their sympatric range. This study helps in our understanding of ecological interactions among Pacific boobies and how selective pressures have shaped the ecomorphology of these seabirds in different ecosystems.