Some Factors Affecting Food Intake and Selection in White-Fronted Geese

It has been shown that most grazing animals are selective in their feeding and that selection can be exercised at different scales. In sheep, for example, there are definite preferences, as measured by the length of time spent on each, for different sward types on hill land (Hunter 1954). On a smaller scale Stapledon (1953) showed that sheep selected particular grass species when given a choice on free range, and Arnold (1960a) demonstrated selection of certain plant parts in relation to their nitrogen and fibre content. Geese select their wintering haunts partly on the basis of their isolation from disturbance and freedom from snow cover. It has already been shown (Owen 1971) that wintering white-fronted geese (Anser a. albifrons Scopoli) select particular vegetation zones within a salting pasture. This paper examines the factors which must be taken into account when considering their selection on a smaller scale. The term 'small scale' includes the selection of particular plant species or parts of plants within a sward. The work is part of a study of feeding ecology carried out over three seasons, 1968-69, 1969-70 and 1970-71 on a flock of up to 7600 European white-fronted geese which spend the period between early November and early March at Slimbridge, on land surrounding the Wildfowl Trust enclosures. Most of the observations were made while the birds were feeding on a salting of approximately 40 ha known as the Dumbles. This area is particularly suitable for feeding behaviour studies as it is favoured by the geese throughout the winter and is overlooked by observatories on the landward edge. The vegetation of the Dumbles can be separated into zones, related to the saltmarsh succession. The Hordeum zone, on the landward (highest) side is characterized by an abundance of Hordeum secalinum Schreb. The Lolium zone, at a slightly lower level has abundant Lolium perenne L. and Agrostis stoloniera L. This gives way to the Agrostis zone with a predominance of Agrostis stolonifera and Puccinellia maritima (Huds.) Parl., which is the lowest grassed area. The Festuca zone is characterized by the abundance of Festuca rubra L. and occupies well-drained sites on the estuary side. Single clone circular patches of Juncus gerardii Lois. occur on the edge of Agrostis and Lolium areas. These make up the Juncus zone. A fuller description of the vegetation is given in Owen (1971). Food selection is a time consuming process and must be balanced against the ability of the animal to ingest sufficient food in the time available. In other words, it is inefficient to select a diet of 100/ better quality if total food intake is thereby reduced by more than 1000. Thus the factors affecting food intake are considered before selection is discussed.