The relative importance of food biomass and quality for patch and habitat choice in Brent Geese Branta bernicla

We studied the relative importance of food biomass and food quality for habitat preference in Brent Geese Branta bernicla by expefimentally manipulating forage parameters. Levels of biomass and ford quality (nitrogen content) were independently enhanced in plots of 2 x 6 m by temporary exclusion from grazing and addition of artificial fertiliser in a full-factorial experiment. Preference was quantified by bit([ density, grazing pressure and interaction frequency Instantaneous intake rate increased linearly with sward height over the range studied. Wild-ranging Brent Geese preferred plots with the highest nitrogen content. These results complement earlier work (Riddington et at. 1997, Hassall et al. 2001, Durant et al. 2004) by demonstrating that food quality is an important parameter determining patch choice and is acting at all biomass levels. Our results support the expectation that patch choice is influenced by nitrogen intake rates. This provides an explanation for distribution patterns of Brent Geese on agricultural grasslands, and the sequence in which pasture and marsh habitats are utilised in spring.