On Encounters Between Wild White-Fronted Geese in Winter Flocks 1)

Detailed observations on large flocks of wild White-fronted Geese (Anser a. albifrons) on the estuary of the River Severn in Gloucestershire, England, during the winters of 1949-50, 1950-51 and 1951-52 serve as the basis for an account of the mechanisms of adjustment employed by these geese when they come into conflict. The winter flocks of White-fronted Geese are large and unstable. Families (parents with young of the year) and pairs of adults form the great majority of persistent groups. Contacts (those conflicts eliciting overt aggressive or submissive behaviour) received particular attention. The outcome of contacts is examined in relation to the status of the contestants, status here indicating membership of an age class (adult or juvenile), a pair, or a family. Two ranking systems are demonstrated: 1. parents> paired adults> juveniles in families > single adults > unattached juveniles, and 2. large families > smaller families. These systems do not determine the outcome of contacts in an invariable way, since other factors influence success. The success of components of a family is affected by the size of the family, even when some members do not take an active part in a contact. It appears that the status of a goose is determined by its membership of a unit, rather than that the status of the unit is determined by any member of it. A large majority of attacks are successful and most are uncontested. About half the contacts recorded affected only two individuals. The remainder mainly affected only two units; very few involved three or more families. The patterns of aggressive and submissive behaviour are described and classified by intensity. A direct relation between intensity of threat and response is found. Though the aggressive postures used by adults and juveniles are similar, adults are more vigorous than juveniles, and parents are more vigorous than adults without families. No connection between intensity of attack and the status of the victim could be established, nor does the response of the victim seem to depend on its own status, but it is affected by the status of the attacker. Males attack more and are more successful than females, though the sexes are alike in the vigour of their attack and in the threats they use. There is very litle fighting within families. Geese of other species are tolerated within flocks of White-fronted Geese. Factors affecting the frequency of contacts include group density, disturbance, access to water and general activity. Direct conflicts for food are rare. There are at least three types of situation producing conflict: sexual rivalry, interference with freedom of movement and preservation of family coherence. Sexual rivalry is connected with the formation of pairs, which probably occurs in winter. Aggressive behaviour is an important means of regulating the movements of geese while feeding. The suggestion that maintenance of the boundaries of a 'moving family territory' is the most important factor causing aggression in geese is disputed.