Vigilance in pre-nesting male geese: mate guarding or predator detection?

Abstract

Several studies have concluded that vigilance decreases with group size. Two main hypotheses for vigilance in males have been proposed: 1) mate guarding (including protection of paternity) and 2) predator detection. Geese often live in large groups and are easy to observe. They are thus prime candidates for studies of male vigilance and agonistic behaviour. In this study, two species of pre-nesting geese were studied. Pink-footed Geese Anser brachyrhynchus were studied on their breeding grounds on Svalbard and in a spring staging area on the northwest coast of Norway, and Bean Geese A. fabalis were studied in a spring staging area in the north-eastern corner of Norway. Observations were made of pairs of geese during foraging bouts, recording foraging, vigilance and agonistic behaviour. Group size, distance between the male and female of a pair, and position in the group (one site only) were also recorded. Few significant relationships were found, the most striking one was that males were more vigilant at the edge of the group than in the centre. In some cases, a non-linear relation was found, i.e. between group size and vigilance in one area. Overall, hypothesis 2) was more strongly supported than hypothesis 1), but most likely the males were making the best of these conflicting interests. The near total absence of a group-size effect was not consistent with the predictions or with earlier findings, indicating that the relations may be more complex than previously suggested.