Scatter Plot from Scientific Research

In 9,559 species with flapping flight, hand-wing index (HWI) increases with maximum elevation (i.e., the highest elevation reported for each species). In a smaller sample (n= 378) of soaring species, HWI initially declines sharply with elevation under 2 km and then increases at higher elevations. However, high HWI in low-elevation species is largely driven by narrow-winged seabirds, in which soaring is often wind-assisted and therefore less constrained by air density. After removing seabirds (seeSTAR Methods), soaring species show a more gradual increase in HWI with elevation (dotted line).

DOI