Concerningly high breeding success rates for the European Starling after a recent invasion in the Neotropics

The European Starling is a highly invasive passerine that recently started to expand throughout South America. Despite its negative impacts on the native fauna, there are no reports of its breeding success, the population recruitment rate, or the factors affecting its nest success in these recently invaded natural habitats. In this study we monitored 100 European Starling nests in a native forest of central-eastern Argentina, during the 2020–2021 and 2021–2022 breeding seasons. We estimated the most common breeding parameters for the population (clutch size, number of fledglings, nest fate, nest survival) and measured nest-site features at different spatial scales to assess if they affected nest survival. Starlings used natural and woodpecker cavities, and nest initiation peak was in September. Successful nests produced ~ 3 fledglings and estimated nest success was 38%. Daily survival rates were negatively affected by nest-tree diameter at breast height. Nest survival was high compared to native cavity-nesting birds. Moreover, the breeding onset as soon as spring begins favors the successful occupancy of cavities by starlings. Here, we provide the first detailed information on the breeding parameters of the starling in South America, which is now available to help in the design of management programs. Given our results, in addition to their effective cavity usurpation behavior, we believe starlings represent a serious threat for endangered native cavity-nesting species and need to be controlled.