Male "macho" mammals exploiting females versus male "Don Juan" birds exploited by females: the opposite-sex exploitation (OSEX) theory

We hypothesize that the general differences in breeding systems between bir ds and mammals results from a different outcome of the between-sex arms rac e. The arms race has been won by male mammals that can impose their mating decision over females, but has been lost by male birds because of the extre me specialization of forearms that do not allow males to trap and hold fema les during copulation. Male birds compensate for their inability to force c opulation by developing "Don Juan" behaviour to persuade females to accept copulation.