Wife Sharing in the Tasmanian Native Hen, Tribonyx mortierii: A Case of Kin Selection?

In the Tasmanian native hen, Tribonyx mortierii, there is an excess of males among immature birds. Permanent breeding groups are established, sometimes of pairs and sometimes of trios; the commonest type of trio consists of two brothers and an unrelated female. The selective forces responsible for the fact that one male will tolerate the presence of the other are analyzed, and shown to depend on the fact that the two males in a trio are brothers.