Alternatively, the wing area gradient may be reversed in macro-scale comparative analyses because higher temperatures and associated thermal uplifts increase the size and diversity of soaring species at lower elevations. Red arrows show opposing elevational gradients—between lowlands and mountaintops—of wing length, hand-wing index (HWI), and hand-wing area (HWA). Bird images are reproduced with permission from Birds of the World (Cornell Lab of Ornithology) and Lynx Nature Books (seeacknowledgments).
