Big changes in backyard birds: An analysis of long-term changes in bird communities in Australia's most populous urban regions

Urban environments are increasingly acknowledged as a priority for biodiversity conservation. Birds in particular are capable of persisting, and sometimes thriving, in cities and towns globally. However, the process of urbanization results in the loss of many bird species due to the resulting changes in habitat conditions. Urban expansion and densification present a threat to both urban bird biodiversity and bird conservation more broadly. Australian urban areas, including suburban and peri-urban areas, currently support moderate bird species richness, but the rapidly changing urban landscape threatens these communities. Unfortunately, many bird species' population trends are not actively studied, resulting in a poor understanding of species persistence in urban environments. Here, we used bird survey data from long-running citizen science databases in a Bayesian List Length Analysis to determine changes in bird species prevalence (the probability of observing a species in a given survey event) over time in Australia's four most populous urban regions. We found that introduced species, historically prominent in Australian urban bird communities, are decreasing in prevalence in all four regions, while a small group of native urban exploiters are becoming more prevalent. Our results also show that many species perceived to be “iconic” or “common” are experiencing declines in prevalence in urban areas, highlighting the importance of monitoring and conservation action in urban areas.