Ecomorphology of Storm-Petrels Along the Pacific Coast of the Americas

For closely related species, differences in morphology can provide insight as to the evolutionary history of a taxonomic group, as well as mechanisms for ecological segregation. Storm-petrels are among the smallest seabirds and their highest 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. This study compares morphological traits related to this foraging behavior in 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 analyze subtle differences in wing shape. Those species that patter the most were found to have a low wing loading, low foot loading, and a long tarsus, and were fairly distinct from the species that were classified as intermediate and least pattering. The DFA and a cluster analysis also identified the behavior of some species as to their pattering abilities for which there was little known observational data. A molecular phylogeny was created from sequencing the mitochondrial ND1 gene. This was used to examine the relationship between the two sub-families of storm petrels as well as to gain insight to the evolutionary history of pattering within the family. There was some evidence for paraphyly between the subfamilies and the morphology associated with an intermediate use of pattering appears to be the ancestral form. A more comprehensive phylogeny using both mitochondrial and nuclear genes in combination with morphological data for more species would help resolve the results of this study

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