Impacts of an invasive plant on bird communities differ along a habitat gradient.
Plants invasions may have important impacts on populations of the native species including birds. We can expect that these impacts will vary in respect to the ecological context where the species live. Consequences of such a variation are, however, still poorly understood. For this purpose, we studied the responses of bird communities to the invasion of Sosnowsky's hogweed (Heracleum sosnowskyi) along a gradient from open to forest habitats in relation to the ecological traits of bird species. The research was conducted in southern Poland in spring 2019. Birds were counted twice on 52 site pairs (control and Heracleum). As expected, the invader had generally negative impact on the total number of birds, their species richness and abundance of all bird guilds except the birds living in the ecotone zone. However, the magnitude of these impacts significantly differed along the habitat gradient: the response of ground dwellers and farmland birds to the invasion was more negative towards open habitats, while the opposite pattern, i.e. a more negative response towards forest habitats, was observed in birds associated with bushes. Individual bird species, however, sometimes differed in the direction and severity of the response to the invasion from the guild to which they belonged. Taken together, our results indicate that the impact of Sosnowsky's hogweed depended on habitats preferred by individual species and whether this alien changed their habitat. This finding should be taken into account when designing management plans for the affected species.