Meeting Abstract
Animals must tune their physical performance to compensate for changing environmental conditions. The breadth of this environmental tolerance may, in turn, contribute to delineating the species’ geographic range. A common environmental challenge that many animals face is life at high elevation, and its characteristic reduction in air density. Flying animals are particularly sensitive to this, as the effectiveness of their lift generation suffers in low air density. Compensation for lower density air must manifest in wing morphology, flight speed or increased power input. While some high elevation fliers have been shown to have relatively larger wings, and thus decreased wing loading (body mass / wing area), there has been less focus on whether and how fliers respond behaviorally. Turkey vultures (Cathartes aura) span a broad geographic range that exposes them to elevations ranging from sea level to >3000 meters. There is no evidence that vultures differ morphologically throughout their range, so they must compensate for air density differences by other means. We used 3-dimensional videography to track turkey vultures flying at two elevations (~120 m and 2200 m) to look for evidence that vultures fly faster at higher elevations, but otherwise exhibit similar gliding performance. After correcting for ambient conditions, we predicted that the high elevation birds would have a 14% faster airspeed, on average, than the low elevation birds, assuming that they are geometrically similar. We found that, indeed, high elevation vultures fly approximately 14% faster. However, the vultures did not differ in their sink rates, suggesting at least partial behavioral compensation for the elevational gradient. Our study highlights how field studies can illuminate the relationship between biomechanical performance and ecology.
