Greylag geese Anser anser – Scirpus maritimus relationships in a newly colonised wintering area in the Camargue (France)

Abstract

In order to evaluate the proportion of Scirpus maritimus tubers consumed by a growing population of wintering Greylag goose (Anser anser) in Camargue, Southern France, we (1) measured the biomass of Scirpus maritimus tubers on the main resting and feeding marsh for geese in the area; and (2) evaluated, on the basis of their feeding behaviour, the consumption of Scirpus maritimus tubers by geese and changes in this consumption in relation to environmental factors. Mean tuber density and biomass were estimated at 7078 tubers per m2 and 0.61 g per tuber, respectively. The mean number of tubers taken per goose per day was estimated at 633 tubers. The foraging efficiency of geese was greatest when birds used head-dip (vs. up-ending) feeding in water depths of approx. 30 cm. Consumption by geese during the winter was estimated at 20.71 tons. Annual consumption by geese (> 50,000 goose-days) represented 1.2% of all tubers present in the whole area. On the basis of these results, we suspect that the marsh could potentially support a number of geese considerably larger than currently present in winter. Nevertheless, the preferential use of some parts of the marsh seems to indicate that parameters other than food availability could also determine geese feeding behaviour.