The selection of winter food by whitefronted geese.
An analysis of the contents of 109 European whitefronted goose (Anser albifrons) fore-guts, and of goose droppings, is described. The diet of the geese in inland pastures in winter consists mainly of grass and forb leaves, but clover stolons and roots, taken when the ground is wet, account for 9%. Leaf fragments in droppings were identified on epidermal cell patterns and a proportion passed through the gut with both leaf surfaces still joined together. This proportion varied from 50% to 90% in different plant species and it is suggested that the proportion of fragments which comprise only a single surface (the breakdown index) is a measure of digestibility. There were differences in the breakdown index of the same plants at different times, probably reflecting changes in nutritional characteristics, particularly in relation to the age of available leaves. Geese showed consistent preferences for some plant species but these were not always related to the nutritional characteristics assessed or to the breakdown index.It is suggested that geese select large patches of food visually or by experience, and that individual species or plant parts are selected when the bill exerts a certain grip which allows some leaves to slip through while others are broken off and ingested. Thus the mechanical properties of plant leaves are the immediate factors governing selection but correlated characteristics of nutritional quality and digestibility are the ultimate factors.