Differential female access to males with large throat patches in the Asian barn swallow Hirundo rustica gutturalis.

Intersexual selection results from several processes, such as differential allocation and differential access, in addition to mating skews by mate choice. These processes can contribute to the evolution, maintenance, and geographic differentiation of male ornamentation, although the importance of these processes in male ornamentation remains poorly understood. The Asian barn swallow Hirundo rustica gutturalis is a socially monogamous songbird that exhibits biparental care and has red throat patches twice as large as those of the nominate H. r. rustica. Our previous study showed that females paired to males with large throat patches had higher reproductive output in terms of multiple broods, although the underlying process resulting in selection for a large throat patch remained unclear. In the present study, we analyzed differential female access to males with large throat patches in H. r. gutturalis. We observed that males with large throat patches acquired older and fatter females, independent of male age class. In addition, females that mated to males with large throat patches returned to the study site more compared with others, indicating the high viability of these females, supporting differential access but not differential allocation. No other measures of male ornaments (i.e., tail length, white tail spots, or throat color value) were linked to female qualities. As these female qualities were associated with female reproductive output, males with large throat patches would obtain reproductive advantages, as found in our previous study. The current findings suggest the importance of differential access for the evolution of a large throat patch in this subspecies.