Cloacal protuberance and copulatory behavior of the Alpine Accentor (Prunella collaris)

I studied the cloacal protuberance and copulatory behavior of the Alpine Accentor (Prunella collaris) over three breeding seasons in central Japan. In males, the seasonal hypertrophy of the glomus seminales forced the posterior wall of the cloaca to form a bulbous cloacal protuberance (16 mm maximum observed diameter) in which sperm were stored. The female’s cloaca also protruded from its original position to form a cylindrical protuberance. Its cloacal lips swelled and turned scarlet. The female’s protuberance remained swollen for an average of 29.3 days, until the last egg in the first clutch was laid. During renesting or the second breeding attempt, female swelling lasted only 9.4 days. The development period of the male’s protuberance was thoroughly overlapped with that of the female. Almost all (98.2% of 431) mating encounters began when the female moved toward the male. In a typical precopulatory sequence, the female exposed the scarlet protuberance toward each of several males in succession, thereby soliciting mountings. Such multiple matings continued throughout the duration of her cloacal swelling. Males performed no sexual displays before they mounted. Each male mated with several females, often in fairly rapid succession, even during the female’s presumed fertile period (defined as the 9 days before the laying of her clutch’s final egg). The unique external sex organs of Alpine Accentors seem to function in their mating system

Masahiko Nakamura, The Auk 107: 284-295. April 1990