Testing multiple pathways for impacts of the non‐native Black‐headed Weaver Ploceus melanocephalus on native birds in Iberia in the early phase of invasion

Not all non‐native species have strong negative impacts on native species. It is desirable to assess whether a non‐native species will have a negative impact at an early stage in the invasion process, when management options such as eradication are still available. Although it may be difficult to detect early impacts of non‐native species, it is necessary to ensure that management decisions can be based on case‐specific scientific evidence. We assess the impacts of a non‐native bird, the Black‐headed Weaver Ploceus melanocephalus, at an early stage in its invasion of the Iberian Peninsula. To do this we identify potential pathways by which competition for shared resources by Black‐headed Weavers could lead to population declines in two ecologically similar native species, and generate hypotheses to test for evidence of competition along these pathways. Black‐headed Weavers could potentially impact native species by displacing them from nesting habitat, or by reducing habitat quality. We found no evidence for either potential competition pathway, suggesting that Black‐headed Weavers do not currently compete with the two native species. However, it is possible that mechanisms that currently allow coexistence may not operate once Black‐headed Weavers reach higher population densities or different habitats.