On the Relation between Herbivore Foraging Efficiency and Plant Standing Crop: An Experiment with Barnacle Geese

Abstract

We test the hypothesis that herbivore foraging efficiency is low at high plant standing crop compared with intermediate levels, which is contrary to conventional theory. Captive barnacle geese were allowed to forage on fields dominated by Festuca rubra. Fields of high and low Festuca biomass were selected, and half of them were mown to reduce plant standing crop artificially. In accordance with our hypothesis, we found that mean short-term intake rate was lowest in vegetation of high standing crop. Daily food intake tended to be lowest at high plant standing crop, but differences were not significant. Despite differences in food intake, we were unable to detect any effect of plant standing crop on body mass change of geese. Festuca standing crop proved to be a poor predictor of either daily intake or mean short-term Food intake. Data were best explained by Festuca cover. We therefore conclude that not Festuca plant standing crop per se, but the actual cover of the forage is of primary importance for grazing geese. We discuss possible constraints on foraging that the geese might have encountered in vegetation of high standing crop.