Variable mating patterns in Tasmanian native hens (Gallinula mortierii): Correlates of reproductive success

Abstract

1. The Tasmanian native hen (Gallinula mortierii) exhibits mate-sharing by both males and females, with monogamy, polyandry, polygyny and polygynandry all occurring in a single population. 2. Multivariate models are used to investigate the relationships between reproductive success and a number of aspects of group compositions and territories in a population of Tasmanian native hens studied at Maria Island, Tasmania, Australia, over five breeding seasons. 3. Mating pattern did not remain a significant explanatory variable in most of the models of the factors affecting reproductive success, suggesting that the reproductive success of individuals is not affected by their mating pattern. The only exception was that mating pattern was significantly related to clutch size, because co-breeding females laid combined clutches. 4. Breeding success (per group, per breeding male and per breeding female) was most significantly related to the total length of edge between short pasture and tall, dense vegetative cover present in a territory. It is proposed that edges between short pasture and cover allow the Tasmanian native hens' precocious chicks to be near good feeding areas while also remaining close to protective cover. 5. Individual components of breeding success were most significantly related to different variables. The presence of water in the territory increased the probability that a group laid eggs. Clutch size was most affected by a group's mating pattern. Hatching success increased with the number of adults in a group. Chick survival increased with the length of pasture/cover edge in a group's territory. 6. The probability that mate-sharing by males occurred in a group was positively related to the total length of pasture/cover edge in the group's territory. There was no such relationship for mate-sharing by females. 7. These models suggest that individuals do not incur any net costs from sharing mates and that such sharing may allow some individuals to breed in higher-quality territories than those to which they would otherwise have access.