Morphological differences relative to ecological segregation in petrels (Family: Procellariidae) of the Southern Ocean and tropical Pacific

We compared eight morphological characters (wing span, wing area, aspect ratio, tail length, bill length, bill depth, tarsus length, and mass of subcutaneous/mesenteric fat) among petrels (family Procellariidae) of tropical versus southern polar avifaunas. Relative to body mass, tropical species have larger wings, bills, and tails, and lighter fat reserves than do polar species. We attributed these differences primarily to adaptations for feeding in markedly different pelagic environments Larger wings, bills, and tails of tropical species enable them to make use of relatively light winds when foraging over wide ocean expanses to exploit sparse and highly mobile and/or volant prey. In contrast, the smaller wings, bills, and tails of polar species enable them to cope with strong winds to exploit highly abundant, less-mobile prey. Greater fat reserves among polar species Probably are an adaptation for surviving extended periods when rough weather (rarely experienced by tropical species) precludes feeding, or for thermoregulation. The most consistent and marked differences between avifaunas are in wing structure and fat load-characters that are directly related to adaptations to physical factors such as wind and climate. Species-specific differences within avifaunas are mostly related to specializations for different foraging habits (i.e. feeding behavior, prey composition, and prey size). Morphological differences and within-species character variances indicated that the tropical ocean is used by a more generalist, migratory group of petrels, whereas the Southern Ocean is used by a more specialized, resident group of petrels.