ON THE RELATION BETWEEN HERBIVORE FORAGING EFFICIENCY AND PLANT STANDING CROP - AN EXPERIMENT WITH BARNACLE GEESE

We test the hypothesis that herbivore foraging efficiency is low at hi gh plant standing crop compared with intermediate levels, which is con trary to conventional theory. Captive barnacle geese were allowed to f orage on fields dominated by Festuca rubra. Fields of high and low Fes tuca biomass were selected, and half of them were mown to reduce plant standing crop artificially. In accordance with our hypothesis, we fou nd that mean short-term intake rate was lowest in vegetation of high s tanding crop. Daily food intake tended to be lowest at high plant stan ding crop, but differences were not significant. Despite differences i n food intake, we were unable to detect any effect of plant standing c rop 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 f orage is of primary importance for grazing geese. We discuss possible constraints on foraging that the geese might have encountered in veget ation of high standing crop.