Maarten J J E Loonen’s scientific contributions

Flocking is a compromise between costs and benefits, and we argue that the degree of benefit depends on individual position within the flock. By continuous observations from a tower, complete film records of all feeding visits by brent geese Branta bernicla bernicla to selected plots during the spring staging season were obtained. Analysis of these films coupled with before-and-after stereo photos of the vegetation confirmed that the vegetation was rapidly depleted, resulting in less than 10 individuals using patches of 800 cm 2 covered by the initially preferred food plant Plantago maritima. The lower level of acceptance appeared related to the intake rate of the alternative food species Puccinellia maritima. The first birds that visited the plots had a higher intake rate and tended to make a different selection from the plants on offer compared with birds at the rear end of the flock. The diet composition appeared a good predictor of the birds' foraging success. The large asymmetries in resource allocation became evident from the use of Plantago; only 12% of the individuals took 50% of the total crop. The film analyses suggested that successful Plantago feeders, which spent long times in rich patches, lost their front position in the flock. To catch-up with the front birds they walked fast while temporarily feeding on Puccinellia. The herbivores studied faced similar problems as many predators do, i.e. their food was distributed in a patchy way and stocks were rapidly depleted. Optimal foraging theory developed for predators is therefore an appropriate tool to understand foraging decisions in herbivores.