The influence of social interactions on the foraging path of Bewick's Swans Cygnus columbianus bewickii
Klaassen, R.H.G. ; Nolet, B.A. ; Bankert, D. - \ 2006
Ardea 94 (2006)3. - ISSN 0373-2266 - p. 477 - 484.
tundra swans - behavior - information - habitat - efficiency - migration - depletion - foragers - patterns - tubers
The efficiency in which high-density food patches are found is determined by the way foragers move between patches. In this study we explore the effect of social interactions on the foraging path, in particular the distance moved between patches. We studied Bewick¿s Swans Cygnus columbianus bewickii that foraged on belowground tubers of Fennel Pondweed Potamogeton pectinatus. We accurately mapped the foraging path of individual swans and determined the distances between visited patches. 24% of inter-patch movements are associated with social interactions. When a swan retreats from a patch because it is chased away by another swan, it moves a significantly larger distance to a patch than if the movement is not associated with a social interaction. Such longer movements are thought to reduce the rate at which high-density patches are encountered, and thus the energy gain rate a swan can achieve. We observed a strong social hierarchy in which families are dominant over pairs and singletons, and pairs are dominant over singletons, which represents a producer¿scrounger model. Singletons were most frequently observed to retreat from patches and are consequently thought to achieve the lowest gain rates, and also as a result exhibit the slowest speed of movement between patches. However singletons might partly compensate for more frequent retreats from patches by moving larger distances to arrive at the front edge of a flock where they encounter unexploited resources.