The social organization of a sexually dimorphic honeyeater: the Crescent Honeyeater Phylidonyris pyrrhoptera , at Wilsons Promontory, Victoria

The social organization of the sexually dimorphic and dichromatic Crescent Honeyeater Phylidonyris pyrrhoptera (Latham 1801) was studied at Wilsons Promontory National Park between January 1994 and January 1997. All breeding attempts at one site were followed during the spring and summer of 1996. Most pairs were multibrooded, with pair‐bonds maintained throughout the study. Breeding males held well‐defined territories. Females, although generally restricting their activities to within their mate’s territory, visited other males’ territories more frequently than did their mates and did so close to the time of egg laying. Males aggressively chased intruding males, but appeared to permit intrusions by non‐mate females. Circumstantial evidence suggests some males may kill neighbour’s nestlings. Female Crescent Honeyeaters are solely responsible for nest construction and incubation. While both sexes attended nestlings, males contributed to parental care significantly less than females. Males also provided significantly less parental care than has been reported for monomorphic species of honeyeater. Single syllable calls are given throughout the year. Peaks in the rate of double and multisyllable calls corresponded with peaks in breeding activity. Only males were observed uttering loud multisyllable calls. In contrast to predictions arising from sexual selection theory and observations of the mating system of sexually dimorphic hummingbirds, the population of Crescent Honeyeaters studied exhibited a socially monogamous mating system. However, the very limited male role in parental care and non‐observance of male territory boundaries by females suggest the genetic mating system may not be one of monogamy.