Exploitation of intertidal Zostera species by Brent geese (Branta berniclahrota): Why dig for your dinner?

Exploitation of intertidal Zostera spp by Pale-bellied Brent geese Branta b ernicla hrota in Strangford Lough, Co. Down, was studied with respect to fe eding method employed, plant parts exploited, the quality of the forage, an d assimilation efficiency. Most Brent geese feeding activity involved diggi ng behaviour, which, along with faecal analyses, indicated that birds were exploiting above (shoot) and below ground portions (rhizome) of the food pl ant. Nutritional information indicated that while rhizome was lower in over all energy, it contained more accessible energy in the form of water solubl e carbohydrate and was lower in indigestible fibre than shoot. Feeding expe riments indicated that Brent geese feeding on whole plants of Zostera nolti i achieved 43% assimilation efficiency. Dig feeding of intertidal Zostera s pp by Brent geese is likely to significantly increase the amount and qualit y of the forage available. Why dig feeding is not employed on all intertida l systems, and its potential effects on the food plants are discussed.