Temporal variation in feeding tactics: exploring the role of competition and predators in wintering dabbling ducks
Guillemain, M. & Fritz, H. 2002: Temporal variation in feeding tactics: exploring the role of competition and predators in wintering dabbling ducks. - Wildl. Biol. 8: 81-90.
To evaluate the effects of competition and predation on foraging by wintering granivorous dabbling ducks, we collected data on long-term changes in foraging methods used during winter in the marshes of western France. Teal Anas crecca, mallard A. platyrhynchos and pintail A. acuta start feeding in shallow areas, and later switch to deeper feeding methods. We show experimentally that the food intake rate is 1.5 times higher in shallow (5 cm) than in deep (35 cm) areas, which may explain why shallow feeding is the principal method used early in the winter season. In the field, the switch between foraging methods was neither related to the frequency of fly-overs by raptors nor to the density of competitors at a foraging site, although birds foraged deeper sooner at sites frequented more often. Thus, the potential role of interference competition remained unclear. Conversely, at each site, the proportion of deep foragers increased with increasing cumulative numbers of foragers, used as a measure of food depletion. We therefore have no evidence that disturbance by predators has an important effect on the foraging methods used, whereas competition through food depletion may play a major role.
Key words: Anas sp., competition, foraging, predation, winter
Matthieu Guillemain* & Hervé Fritz, Centre d’Etudes Biologiques de Chizé - CNRS UPR 1934, 79360 Beauvoir-sur-Niort, France - e-mail adresses: m.guillemain@oncfs.gouv.fr (Matthieu Guillemain); fritzh@cebc.cnrs.fr (Hervé Fritz)
*Present address: Office National de la Chasse et de la Faune Sauvage, CNERA Avifaune migratrice, La Tour du Valat, Le Sambuc, F-13200 Arles, France
Corresponding author: Matthieu Guillemain
Received 27 February 2001, accepted 29 June 2001
Associate Editor: Hannu Pöysä