Aggressive interactions in Swan Geese Anser cygnoides and their hybrids

Abstract

Evidence for direct interspecific competition in wildfowl and between hybrids and their parent species is scarce. This study examined threat displays and agonistic encounters (n = 324) in a goose flock of 140 Swan Geese and 13 hybrids with Greylag Goose living in Heidelberg, SW Germany. In general, agonistic behaviour made up less than 1% of the time budget throughout the year as measured by focal animal sampling. Most encounters (84%) were won by the initiator, both in Swan Geese and in hybrids. No difference was found between Swan Geese and hybrids in the outcome of an encounter, suggesting equal competitive quality. There were differences with respect to threat postures with hybrids performing diagonal neck threats more often and intentional movements less often. This seems to be related to their hybrid origin, since Greylag Geese most often show diagonal neck and forward threat displays. There was no direct evidence for hybrid superiority or inferiority.