Management of alien bird impacts does not reflect their severity

Biological invasions can harm biodiversity – indeed, they are a principal cause of native species extinctions (Bellard et al. 2016. Alien species as a driver of recent extinctions. Biol. Lett. 12:20150623). Biological invasions occur worldwide – whilst some of their impacts are managed, others are not. Identifying drivers of management actions may reveal why some impacts remain unmanaged, informing strategies to improve management consistency. We identified factors that influence actions to protect native animals from the biodiversity impacts of alien birds. We reviewed literature to identify impacts, categorising them as unmanaged or managed (irrespective of management success). For each impact, we collected data on variables hypothesised to influence management, including characteristics of affected native species (e.g., endemism) and alien species (e.g., years resident as an alien); characteristics of impacts (e.g., their severity – how harmful they are to native species, as measured using a published framework); and characteristics of the environment (e.g., human population density). We used binomial mixed effects models to identify associations between variables and management. Intuitively, actions to manage alien bird impacts tend to focus on the protection of endemic species. However, they do not focus on the most severe impacts, nor the most threatened native species. Indeed, feasibility influences actions, whereby long-established alien bird populations with damaging biodiversity impacts remain unmanaged, most likely because these long-established populations tend to be large and widespread and hence are considered too difficult or costly to manage. Timely interventions are crucial to prevent the damaging biodiversity impacts of biological invasions from becoming unmanageable.