Response of birds to episodic summer rainfall in the Great Western Woodlands, Western Australia

From 1999 to 2003, the Great Western Woodlands in Western Australia experienced above average summer and autumn rainfall. Although rainfall from 2004 to 2010 approximated long-term seasonal and annual averages, the soil and litter layer became parched, there was less vegetative growth, and nectar production declined. As habitats became drier, fewer birds nested, although some bred and fledged young. Ground, shrub, and canopy foragers, including migrants, along with nectar-feeders declined in abundance. The numbers of raptors and cuckoos declined in line with declines in abundances of prey and host species. Declines in abundance and breeding were probably linked to declines in food resources, although there were no consistent changes in the foraging behaviour of birds. There was a modest recovery in breeding effort and species abundances in 2010 following above average rainfall in the spring and summer of 2008/2009. These observations indicate that productivity and avian abundance in these semiarid woodlands (200-300 mm annual rain) decline with average rainfall. Episodes of high and possibly prolonged rainfall are required to restore productivity and allow faunal populations to recover. Climate change models predict less rain and higher temperatures in southwestern Australia. High rainfall events will occur, but there will be longer intervals of average or below average rainfall. As shown by events in 2010, birds can respond quickly to increased rainfall, but with longer periods of drier or even average rainfall numbers may fall to levels below which recovery is not possible. Populations in less productive habitats will disappear and the distribution of species will become increasingly patchy, with increased likelihood of local extinction. To reduce these heightened risks associated with anthropogenic climate change habitat connectivity must be maintained on regional and continental scales not presently provided by existing conservation reserves