The social organization and mating system of the Striated Grasswren

This paper summarizes the breeding biology, social organization, and mating system of the Striated Grasswren (Amytornis striatus), a member of one of the least-known genera of Australian passerines, the grasswrens. I studied 18 color-banded groups and 14 nests in South Australia for one breeding sea son in 1996. Mean territory size was 3.0 ha, and territories consisted of s andy dunes dominated by spinifex (Triodea irritans). This apparent dependen cy on mature spinifex, coupled with poor dispersal ability, suggests that t hr Striated Grasswren is particularly susceptible habitat destruction. Most groups consisted of socially monogamous pairs, mean group size was 2.1 adu lts, and the adult sex ratio was 0.95 (males:females). The average clutch s ize was 2.2 +/- 0.4 eggs and an average of 1.1 +/- 1.1 young fledged per ne sting effort. A male and a female provided similar amounts of parental care at a single nest. Cloacal protuberance size and amount of sperm collected did not suggest intense sperm competition among males.