 Males sing constantly as the breeding period approaches and perform less often once pairs have bonded . In the presence of a female , a male sometimes flies to his nest and sings from the entrance , apparently attempting to entice the female in . Older birds tend to have a wider repertoire than younger ones . Those males that engage in longer bouts of singing and that have wider <unk> attract mates earlier and have greater reproductive success than others . Females appear to prefer mates with more complex songs , perhaps because this indicates greater experience or longevity . Having a complex song is also useful in defending a territory and <unk> less experienced males from encroaching . 
