Selective foraging of alpine marmots in alpine meadows [Affouragement sélectif des marmottes alpines dans les prairies alpines].

Résumé

Foraging of a familial group of Alpine marmot (Marmota marmota) was studied in an Alpine meadow (2,400 m) in Savoie (France) during the summer 1991. The aim of the study was to describe the type of food use in relation to the time in year through a microhistological examination of fecal pellets collected in the study area during three months and a vegetation sampling in the home range of the group. Plant fragments and plant items were classified to species only for dicotyledons. Alpine marmots prefer forb species (88%) over graminoids (10%). They prefer flowers and inflorescences (respectively 52 et 6%) than leaves and stems. The proportion of graminoids and of inflorescences in fecal samples decreased significantly from July to September, when proportion of seeds increased, even if their abundance was still low. Licking of schist surfaces was observed. This behaviour was attributed to mineral deficiency. The most commonly occuring plant fragment over the three months (28, 19, 24% of all items) was an unidentified dicotyledon flower. The two other most common plant fragments were leguminous : vegetative parts of Astragalus montanus, (12, 14 et 14%) and flowers of Oxytropis gaudini (2, 11 et 14%). Graminoids were more abundant than forbs during the three months. Marmots do not feed on all items in proportion to their abundance. Among the 49 forb species found on this home range, only 9 were identified in fecal analysis. With the exception of Astragalus, the eight other species had low or very low covering rate and were situated far from the main burrow. Results indicated that Alpine marmots choose their food plants and select mostly forb flowers. Forbs, especially leguminous, have a higher mineral content and a higher protein content than grasses. Food selectivity is affected by phenology of the plant species, diet superiority and avoidance of plant secondary compounds. This selectivity would explain that marmots spend a great proportion of their foraging time in searching and that cohesion of the members of the familial group is low during foraging. Similar results have been found with Marmota caligata, Marmota flaviventris and Marmota monax.