Waterbird abundance in eastern Australia, 1983-92

We examined the relationships between abundance of 16 species of waterbirds and the rainfall in eastern Australia, the rainfall west of this region, the annual Southern Oscillation index (SOI), the wetland area, and hunting in eastern Australia for the period 1983-92. Data were collected during aerial surveys of eastern Australia. For most explanatory variables, lags of up to five years before aerial surveys were also investigated during these analyses. The analyses covered all nine game species (plumed whistling-duck, Australian shelduck, Australian wood duck, pink-eared duck, grey teal, chestnut teal, Pacific black duck, Australasian shoveler, hardhead) and seven non-game species (Australian pelican, white-faced heron, yellow-billed spoonbill, freckled duck, black swan, black-winged stilt, red-necked avocet). Regression models were developed for all species apart from Australian pelicans. Rainfall and climate indices generally were most correlated with the species' abundance. Bonferroni adjustments to significance levels meant that there were significant variables in regression models for seven of the 16 species. Abundance indices for plumed whistling-duck, chestnut teal, hardhead, black swan and black-winged stilt were related to the climate variables (rainfall, SOI) and wetland area, whereas abundance of pink-eared duck and red-necked avocets were negatively related. Abundance of chestnut teal was positively related to numbers of hunting licences sold. The results are equivocal about the role of hunting in determining waterfowl abundance, which is probably a reflection of few data points and numbers of variables included. In general, abundance indices of waterbirds appear to have decreased between 1983 and 1992, which may correspond to other factors not modelled.