Female splendid and variegated fairy-wrens display different strategies during territory defence

•Both splendid and variegated fairy-wren females sang songs as complex as males.•Only splendid fairy-wren females shared more elements with their mate.•Females in each species adopted different strategies when responding to intruders.•Female splendid fairy-wrens competed with female intruders.•Male and female variegated fairy-wrens coordinated responses against male intruders.

Contrary to the traditional view that territory defence is a male behaviour, there is now evidence that female birds actively engage in territory defence, either alone or with their mate. In males, song sharing between neighbours has been shown to facilitate territory defence, but little is known about the importance of song sharing for such behaviour in females. Here, I examined sex roles and song element sharing in two related species: the splendid fairy-wren, Malurus splendens, and the variegated fairy-wren, Malurus lamberti. I first described song structure and song element sharing between partners and neighbours in both male and female songs. I then simulated conspecific intrusions by broadcasting a female or a male song within a pair's territory. Both splendid and variegated fairy-wren females sang songs as complex as their male counterparts and responded to playback of simulated conspecific intrusions. Song element sharing with neighbours was common in both species, but only splendid fairy-wren females shared more elements with their mate than with other recorded males on average. Females in each species engaged in different strategies when responding to territory intruders: female splendid fairy-wrens competed with female intruders, while variegated fairy-wren females coordinated their defence with their mates and exhibited cooperative defence behaviours toward male intruders. I discuss the ideas that variation in levels of extrapair paternity and/or female competition may drive the evolution of different female strategies when responding to territory intruders.