Food selection by barnacle geese (Branta leucopsis) in an Arctic pre-breeding area

Detailed patterns of food selection by pre-breeding barnacle geese (Branta leucopsis) were investigated in Varsolbukta, western Spitsbergen, Svalbard, in moss-dominated vegetation. This habitat is favoured by geese during the early Arctic spring when grass abundance is low. Grass is more profitable food than moss in terms of nutrient content and digestibility, and a five-fold higher proportion of grass in geese faeces compared with other vegetation indicated that geese selected grass in spite of its low availability compared with moss. As profitability may also depend on various properties that enhance searching efficiency, we studied the effects of grass tiller size, density and patchiness on goose selectivity in an experiment comparing ungrazed vegetation with vegetation where geese were allowed to feed for controlled periods of time. Large (two-leaved) tillers provided more biomass than small (one-leaved) tillers. The abundance of ungrazed large tillers relative to small tillers was lower in the grazed plots than in the ungrazed control plots, indicating that the geese preferred large tillers. Grass tiller density or spatial tiller distribution did not affect the degree of selectivity of geese for grass. Thus, we suggest that the feeding strategy of the geese in the early Arctic spring is primarily driven by the degree of tiller conspicuousness, as determined by tiller size. Furthermore, we suggest that an intense time allocation to feeding and an enhanced quality of grasses compared with mosses enabled geese to profit from feeding on the scarce grasses.