Abstract
Plant invasions alter bird community composition worldwide, but the underlying mechanisms still require exploration. The investigation of feeding guild structure of bird communities can be informative in respect to the potential impact of invasion features on the availability of food for birds.
For this purpose, we focused on determining the influence of the invasive Sosnowsky's Hogweed Heracleum sosnowskyi on the abundance of birds from various feeding guilds. In spring and summer 2019, birds were counted three times on 52 pairs of sites (control + Heracleum) in southern Poland, at various stages of Sosnowsky's Hogweed development (i.e. sprouting, full growth and flowering, all corresponding to respective bird counts).
We have shown that the presence of invader negatively affected the abundance of birds from all feeding guilds. However, a closer examination of the invaded sites uncovered that responses of particular guilds differed in respect to development stages expressed by a set of characteristics of the invader.
Ground and herb insectivores were more common on plots with a higher number of the invader, while the abundance of bush and tree insectivores was negatively correlated with hogweeds' height. Granivores were not affected by the invader's features, while the abundance of omnivores was negatively related to the number of flowering hogweeds.
Besides showing the general negative impact of the invader on different feeding guilds, our research has shown that certain aspects of Sosnowsky's Hogweed invasion may support or depress occurrence of different birds on invaded plots. Knowledge of these aspects may facilitate our capacity for coping with challenges the invasive plants put in front of bird conservationists.