How aggressive are Egyptian Geese Alopochen aegyptiaca? Interactions with Greylag Geese Anser anser and other birds in an urban environment

Abstract

Under European Union legislation, the Egyptian Goose Alopochen aegyptiaca is listed as an invasive species of concern to member states, because of the adverse impacts which it has on native species. One of the reasons for this classification is interspecific competition, and the supposed aggressiveness of Egyptian Geese towards other birds, yet there are few data published on this behaviour. Here we compare the agonistic behaviour of Egyptian Geese with that of resident Greylag Geese Anser anser in a recently colonised urban area of southern Germany. For both species, aggression consisted mostly of a threat posture with extended neck (95.8% of Greylag Goose threats; 97.8% of Egyptian Goose threats), whilst hissing regardless of neck posture occurred only occasionally (3.8% in Greylag Geese; 1% in Egyptian Geese). Threatened birds mostly avoided the opponent, and encounters rarely resulted in a physical fight (0.4% in Greylag Geese; 2.4% in Egyptian Geese). Intraspecific aggression was significantly more frequent among Egyptian Geese than among Greylag Geese occurring in the same area, but the overall frequency of interspecific aggression did not differ between the two species. There were, however, differences in the species affected: among Greylag Geese, the most frequent targets of interspecific aggression were Egyptian Geese, whereas Mallard Anas plathyrhynchos were most frequently targeted by Egyptian Geese.