Weather Affects Competitive Ability in a Guild of Soaring Birds

SHEPARD, E.L.C.; LAMBERTUCCI, S.A.

Bariloche

Congreso; I Worldwide Raptor Conference; 2013

Area-use in animals is typically examined in relation to the distribution of food and associated habitat variables. For soaring birds this may be only half the story, as the availability of rising air is a key determinant of the ability of these animals to move. We refer to environmentally driven changes in flight costs as the ?energy landscape? and suggest that this has far-reaching implications for soaring birds, influencing the locations and times where they can operate and the circumstances under which given species may enjoy a competitive advantage. We used aeronautical models to examine this in a guild of New World scavenging birds. Results suggest that movement costs vary according to morphology (specifically wing loading) and weather variables, with Andean Condors (Vultur gryphus) performing better in strong updrafts and moderate to high winds. Spatial trends in meteorological factors seem to confine condors to the mountains (a trend that is borne out in worldwide distributions of condors and other large soaring birds), where they out-compete smaller species. However, both model predictions and carcass observations suggest the competitive ability of soaring birds varies according to meteorological conditions in areas where distributions overlap. This challenges the view that scavenging guilds are structured by fixed patterns of dominance and suggests that competitive ability varies across spatial and temporal scales, which may ultimately be a mechanism promoting diversity among aerial scavengers.