Greylag Goose (Anser anser) Science Article 4
Just after arrival in early autumn, Greylag Geese Anser anser wintering in the Marismas of the Guadalquivir (SW Spain) concentrated on Scirpus litoralis areas, but moved to Scirpus maritimus areas as soon as these zones were flooded after autumn rains. In both Scirpus habitats the diet was dominated by tubers of these plants, but during the late winter there was an increase in the consumption of green parts. The tubers of Scirpus have high concentrations of both soluble carbohydrates and fibre, but low concentrations of protein and minerals. Adequate quantities of the essential nutrients seem to be acquired by switching to foraging on pastures. In spite of their relative high protein and low fiber contents, S. litoralis tubers were less preferred than those of S. maritimus. The reason for this is that geese need more time to forage on S. litoralis tubers. In the S. maritimus habitat type the geese may spend more time on other activities and vigilance.
Amat J.A., Garciacriado B. & Garciaciudad A, ARDEA 79 (2): 271-282.