Trends in avian diversity and abundance in remnant vegetation in inland eastern Australian farmland between 2014 and 2023

Australian bird communities fluctuate greatly in composition and abundance in response to rainfall. At the same time, increasing numbers of threatened bird species are declining in abundance and range, due to various threatening processes. An opportunity to study the dynamics of avian communities in inland eastern Australia arose when birds were surveyed in remnant floodplain vegetation on cotton farms in spring (September–November) 2014 and again in spring 2023, mostly at the same sites (197 sites in 2014, 195 in 2023 and 167 in common). Sites were censused twice on different mornings by separate observers in both years, with 133 diurnal landbird species and 4384 individuals recorded in 2014, and 151 species and 8227 individuals in 2023. Mean (± SE) species richness and total abundance of landbirds were 10.9 ± 0.03 and 22.3 ± 0.08 per 2-ha site, respectively, in 2014, and 17.8 ± 0.04 and 42.4 ± 0.13 per site, respectively, in 2023. Birds were almost twice as abundant in 2023 as 2014, likely attributable to 3 years of above-average rainfall in 2020–22. By contrast, the 2014 surveys were preceded by 1.5 years of average or below-average rainfall. Most (104) of the 126 species recorded in both years were more frequent in 2023 than 2014. Of concern, however, were four sedentary and ‘declining’ woodland species in south-eastern Australia that were either not recorded in 2023 or were less widespread or abundant than in 2014: Speckled Warbler,* 8 Varied Sittella, Crested Shriketit and Crested Bellbird. Introduced species were also more prevalent in 2023 than 2014, with Common Myna increasing greatly in the intervening 9 years. Our findings accord with the rainfall-driven variability of Australian bird communities, help prioritise the species most in need of recovery interventions, and focus attention on the impact of the rapid increase of the Common Myna in inland eastern Australia.