Utilization, diet and diet selection by brent geese Branta bernicla bernicla on salt-marshes in Norfolk


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    RSPB, Etive House, Beechwood Park, Inverness, Scotland


The diet and utilization by brent geese of two plant communities (Limonium/Armeria marsh—a short sward community in the upper mid salt-marsh and composed of several species, and Salicornia marsh—a community of the lower salt-marsh dominated by Salicornia europuea agg. and Aster tripolium) were studied on the north Norfolk coast. The biomass on these communities was highest in autumn and declined markedly in November owing to the senescence and die-off of the succulent species. This decline was not significantly precipitated by the grazing of the geese but coincided with their switch to inland habitats where the biomass m-2 and total food available on fields of winter wheat and grassland within the population's home range was 20–30 times greater. Brent geese continued to graze salt-marsh at a low intensity through the winter, feeding largely on Puccinellia maritima. In spring they returned largely to Limonium/Armeria marsh where they significantly reduced the regrowth of Puccinellia maritima.

The main plant species ealen was Puccinellia maritima, especially in mid winter. Salicornia maritima agg. leaves and seeds formed much of the diet in autumn, whereas Triglochin maritima, Plantago maritima and Aster tripolium were important foods on Limonium/Armeria marsh in spring. All these species were selected at some part of the year. Selection was related to the proline (an imino acid used by salt-marsh plants as an osmoregulator) and chloride content and avoidance related to tannins. Two species which contained condensed tannins. Limonium vulgare and Armeria maritima, were rarely eaten. As well as being a nutrient, proline may help to neutralize the effects of tannins in the diet if incorporated into proline-rich proteins.