Ecomorphological differences in foraging and pattering behavior among storm-petrels in the eastern Pacific Ocean

Abstract

For closely related species, differences in morphology can provide insight into the evolutionary history of a taxonomic group, as well as mechanisms for ecological segregation. Storm-petrels are among the smallest seabirds, and their greatest taxonomic diversity occurs in the eastern Pacific Ocean. Some storm-petrels exhibit a unique foraging behavior, known as "pattering" or "sea-anchor soaring," in which they appear to walk on the surface of the ocean, but this behavior is used to a varying degree among species. We compared morphological traits related to the pattering behavior in 9 species of storm-petrels that breed in the eastern Pacific. Measurements on the wing (wing loading, aspect ratio), beak (size), and leg (length and foot size) were analyzed using a discriminant function analysis (DFA). A thin-plate spline/relative warp analysis was also used to detect subtle differences in wing shape. Species that patter the most have low wing loading, low foot loading, and a long tarsus and were distinct from the species that were classified as intermediate or least pattering. The DFA and a cluster analysis also identified putative pattering behavior of species based on morphology, for which there was little known observational data. A molecular phylogeny of the mitochondrial ND1 gene revealed that the 2 subfamilies of storm-petrels were not monophyletic. The phylogenetic tree shows that the pattering behavior has a strong evolutionary signal and arose early among storm-petrels.