Monitoring the occurrence of invasive alien species and their impact on the population size of the greylag goose (Anas anser, L. 1758) in a selected Natura 2000 area in Poland

Given the significant expansion of alien predator species that may negatively affect native animal species, especially waterbirds, this study undertook an analysis of the occurrence of American mink (Neogale vison), raccoon dog (Nyctereutes procyonoides) and raccoon (Procyon lotor) in the Natura 2000 – Wełtyńskie Lakes area of 2811.2 ha, and an assessment of the impact of these animals on the occurrence of the greylag goose (Anas anser). A camera trapping inventory for the three non-native carnivore species was carried out from April to September 2022, parallel to the inventory of the greylag goose. Results confirmed the presence of all three non-native species in the analyzed area. Among the species, raccoons were characterized by the highest population size, density rate and reproductive success. At the same time, a declining population of the greylag goose was found compared to the previous breeding season. This population achieved low breeding success.