Assessment of food intake rates in pink-footed geese Anser brachyrhynchus based on examination of oesophagus contents

An alternative to the so-called 'marker substance' method used to estimate daily food intake in geese is presented. Based on the assumption that a gra zing bird takes one leaf per peck, the daily food intake rate can be calcul ated by multiplying mean bite weight, peck rate and total daily foraging ti me. Wintering pink-footed geese Anser brachyrhynchus feeding on pastures an d winter wheat fields were collected and samples of leaves in the oesophagu s were measured, dried and weighed individually. We measured leaf lengths i n unexploited areas of the same fields upon which geese had been feeding. P eck rates of winter wheat feeding geese were measured. Daily foraging time was obtained from observations of activity budgets of flocks of geese. Dail y food intake of winter wheat feeding geese was estimated at 159-229 g ash free dry weight (AFDW) during late winter and at 188-212 g AFDW in early sp ring. For geese feeding on pastures in early spring food intake was estimat ed at 170 g AFDW. Averages were generally in accordance with estimates deri ved by the 'marker substance' method. Bite length was positively related to primary leaf length of winter wheat, suggesting that geese adjust bite siz e to available leaf lengths. There was a negative relationship between peck rate and length of all leaf types, but the relationship was only significa nt for primary leaves. Based on the assumption that bite length was identic al to primary leaf length and the relationship between primary leaf length and peck rate, a quadratic relation between primary leaf length and instant aneous intake rates was derived, yielding a peak intake rate of 0.62 g AFDW min(-1) at a primary leaf length of 8.4 cm. In the beginning of the winter , bite lengths were close to this optimal leaf length, but decreased during winter.