Outcomes of community-led urban rat control on avifauna

Cities are increasingly recognised as important sites for biodiversity and essential for improving human-nature connections. However, urban areas are also hotspots for rats, which negatively impact biodiversity due to competition and depredation. Urban residents may undertake rat control on their properties, but the effectiveness of such volunteer initiatives for broader biodiversity outcomes has not been tested in urban environments. We conducted a comprehensive study inclusive of rat abundance, adult bird diversity, and bird breeding success. We monitored rat (Norway rat Rattus norvegicus; ship rat Rattus rattus) presence and modelled detection probabilities and occupancy in suburban residential backyards in Auckland, New Zealand. We also compared bird abundance and richness among backyards and recorded 140 nesting attempts from 15 bird species between September 2021 and February 2022. Despite rat control, rats were detected at some point in all backyards, though relative abundance was low, and fewer rats were detected in backyards with more frequent rat control. Higher bird abundance, and to a lesser extent richness, were associated with proximity to native vegetation patches and more frequent rat control. Overall fledging success was relatively high and predation by rats was relatively low compared to previous research. Nest survival was slightly higher for introduced bird species. Daily nest survival rate increased with nest height, proximity to native vegetation patches, and when rat detection rates decreased. Although the effect was small, frequent rat control within a backyard was associated with increased fledging success and increased bird species richness and abundance. Further research is required to explore the factors that interact with backyard rat control to improve local outcomes for birds. High levels of community participation in backyard rat control are required to improve neighbourhood-wide outcomes for birds.