Are communal pukeko caught in the prisoner's dilemma?

Summary

The prisoner's dilemma of game theory provides a possible explanation for communal breeding in the pukeko (Porphyrio porphyrio, Aves) where group breeding birds are at a reproductive disavantag compared to pairs. Territorial defence is largely the realm of males. A male who ‘defect’ on neighbours by taking in an extra male defender and so becoming communal stands to gain territorial area and possibly higher reproductive success. Neighbours are forced to follow suit if additional males are available or lose their territory and therefore their breeding opportunities. If neighbours also admit an extra defender, the initial ‘defector’ loses his advantages and all males end up with the lower breeding success of communal groups. Such ‘defection’ to a communal habit appears to be the only stable solution.