Socio-ecology of the Grey-crowned Babbler: population structure, unit size and vegetation correlates

Summary

An intensive study of a population of Grey-crowned Babblers comprising nearly 300 birds in 46 social units was carried out in Queensland, Australia. This paper describes the population, the study area, and its vegetation with special attention to relationships between group size, age structure and vegetation. Individuals lived in units of 2 to 13 (Fig. 2) composed of a breeding pair and up to 11 non-breeders.

Iris color, described in the Munsell system, was used for age determination. The population was composed mainly of yellow-eyed breeders and brown-eyed, yearling non-breeders (Fig. 3). Older breeders tended to be in larger units (Fig. 5) and mated to each other rather than to younger breeders (Table 3). Unit size was correlated with characteristics of vegetation on the territories. Smaller units were more variable in vegetation than larger units (Fig. 6). The correlation of some vegetation indices with unit size was lowest near the nest (Fig. 7). Vegetation was loosely correlated with breeder iris color, hence age (Table 5).