Trends in timing of migration of south-western Australian birds and their relationship to climate

The influence of climate on the timing of migration of Australian birds is poorly understood, particularly in Western Australia and for waterfowl. This paper examines a new dataset, comprising presence–absence records of 20 species of waterbirds and landbirds at Middlesex, south-western Australia, for the period 1973–2000. Considering only species with sufficient records to determine trends, over this period nine of 19 species (47%) had significantly altered arrival times (five arriving earlier and four later); seven of 17 species (41%) had significant changes in departure dates (four departing later, three earlier); and eight of 17 (47%) species had significantly different season lengths (the period spent at Middlesex, with five spending more time at Middlesex). Generally, changes in the timing of regular seasonal movements were consistent among species that arrived or departed in similar seasons, with species that arrive in spring tending to arrive earlier, while species arriving in autumn and winter arrived later. Trends were generally more pronounced in spring-arriving species, though strong trends were also seen in other seasons. This region experienced significant reductions in the number of rain-days and increased minimum temperature over the study period. For many Middlesex species, particularly waterbirds, precipitation changes appeared to have a greater influence on changes in migration timing than temperature, though some species also appeared to respond to changes in extreme temperatures. This differs from many northern hemisphere studies, where changes in mean, maximum, or minimum temperature were associated with changes in migration timing.