LOOSJES M (1974) Habitat use, disturbances and food of Greylag Geese Anser anser in a brackish tidal area. LIMOSA 47 (3): 121-143.

Greylag Goose Anser anser On the habitat-use, disturbances and food of Greylag Geese Anser anser in a brackish tidal area. The habitat-use and the food of Greylag Geese was studied on the Beninger Slikken in the Southwestern part of the Netherlands, mainly during the months January to March 1969 inclusive. The Beninger Slikken form a part of an, in the meantime dammed-up, estuary. It contained brackish water and had a tidal difference of about 2 metres (7 feet). The vegetation consisted mainly of reed Phragmites communis, Scirpus lacustris glaucus, and sea club-rush Scirpus maritimus. Quantitative data were collected on the habitat-types where the geese were staying and on their behaviour in these habitats, depending on the time of day and the tide. In addition, data were gathered about the causes and consequences of disturbing influences and about the consumed and available amount of food. The Beninger Slikken were for the Greylag Geese of importance especially as a wintering area, obviously as a consequence of the regular flooding by brackish water. The total number of geese-days in the winter of 1968-1969 was approximately 400.000 The winter-population was rather isolated from other populations of Greylag Geese in the surroundings. The distribution of the geese over the various habitat-types (water, mud-flats and rushes with or without some water) was, apart from the disturbance by shooting, independent of the time of day. However, there is an obvious relation between this distribution and the tidal movements. This is mainly based on the availability of the types of habitat, further on effects of disturbance and on a preference of the geese for rushes with some water, over dry rush-areas. The difference between this distribution as found in an area with Scirpus lacustris and as found in an area with Scirpus maritimus, are based on differences in elevation and inclination in the area, and in disturbances. Feeding occurs mostly in the morning. On an average, one third of the geese feeds during day-time, during the night less feeding takes place and during very dark nights there is no feeding at all. The occurrence of different kinds of behaviour appears to depend not only on day-rhythm but mostly on the availability of the various types of habitat as a consequence of the tides. The geese feed preferably in a rush-area, with a little water. They can feed in water up to 3 dm (1 foot) deep. Rootparts of the rush can then still be drawn loose while swimming and grubbing. The geese sleep in principle in a dry rush-area, however, often on mudflats because of disturbance. Voluntary dispersal within the Beninger Slikken generally showed no fixed pattern. The geese flee in case of disturbance to the mudflats or to the adjoining water, or, in case of a serious disturbance, to adjacent mudflats. Disturbing factors are especially hunting and the sight of planes. During day-time the geese are on an average disturbed one third of the time, and they have to flee four times a day. In stormy weather with high tide the geese flee to grass-land on the outside of the dikes. Food consists almost exclusively of root-pieces of Scirpus lacustris and tubers of Scirpus maritimus. Especially when there is lYz to 3 dm (one half to 1 foot) of water on the rush, the geese, while foraging, trample at times with their legs on the place where they excavate the roots. 185 ? 25 root-pieces are eaten per goose per 24 hours (mean and 95% confidence limits), while foraging for more than 5Yz hours. This amounts to a quantity of food of approximately 0,8 kg. Total consumption during the winter of 1968-1969 has been estimated at (75 ? 10).106 root-pieces, whereas without overgrazing, at least 380.106 root-pieces could be eaten. Damage to the rush-culture can be expected when the geese are dispersed extremely irregularly over the area due to systematic disturbances. Probably the geese fulfil a positive function by thinning out the rushes. The carrying capacity of a rush-area is, with respect to the food-supply, 30.000 ? 8.000 geese--days per hectare. It is possible that the mutual distance required by the geese on the rush is in fact the limiting factor. The recent damming up of the estuary, autumn 1970, will hav,e harmful effects because of freshening up, probable increased pollution, ceasing of the tides and an increase of disturbing factors. Other threats are an increase of recreation, industrialisation and aerial traffic and a decrease of refuge possibilities. By executing new measures for management based on research, by furnishing new areas and by utilizing the possibilities for adaptation of the Greylag Geese, we may try to preserve this species for Western Europe, in the present numbers.

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