Male aerial display and reversed sexual size dimorphism in the dunlin

Abstract Reversed sexual size dimorphism, with males smaller than females, is common in waders. The aerial display hypothesis suggests that sexual selection in males favours aerial agility, and hence small size, in species with male display flights. We tested this hypothesis in the dunlin, Calidris alpina Display flights were uncommon in the early breeding season but increased markedly when females began laying. Male display areas were largely overlapping, and display flight seemed to be mainly an advertising signal to potential mates. Display rate, as well as proportion of time spent in aerial display, increased with decreasing male size. During aerial display, small males also performed costly hovering flights more often and for relatively longer than large males. These results support the aerial display hypothesis.