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Autumn feeding ecology of herbivorous wildfowl in the danish wadden sea and impact of food supplies and shooting on movements



Autumn feeding ecology of herbivorous wildfowl in the danish wadden sea and impact of food supplies and shooting on movements



Danish Review of Game Biology 13(4): 2-32



The southern part of the Danish Wadden Sea is an important autumn staging area for Brent Geese (peak numbers 6,000), Wigeon (15,000) and Teal (3,500). In autumn 1985 and 1986 their ecology and movements were studied in relation to food availability and shooting activity. In September-October the wildfowl fed in the tidal zones on a 138 ha Zostera bed. Due to the tide they could only feed from 3 hours before to 3 hours after low tide, and to fulfill their daily energy demands the birds also fed during nightly low water periods. During autumn the above-ground Zostera resources were reduced from 39 tons to 1 ton, the grazing by wildfowl accounting for the major part of the losses. In consequence, feeding efficiency of Brent Geese and Wigeon was hampered. Brent Geese switched to below-ground parts of Zostera, Wigeon abandoned the area. Interspecific exploitative competition became acute, with Brent Goose as the best coping species of the two. In 1985 duck shooting on the mud flats was moderate; in 1986, however, it was intensified displacing the ducks and geese to the southern part of the Zostera bed, which is part of a non-shooting zone. This zone was soon depleted for resources, and the majority of the wildfowl were forced to leave the area earlier than in 1985 even through food was still available in the shooting zone. At night the birds fed in the shooting zone. When the ducks had abandoned the area, shooting ceased, and the protected Brent Goose could remain undisturbed for the rest of the autumn. In October a concentration of ducks built up in the non-shooting zone at the Romo barrage. Here the ducks consumed ripening Suaeda and Atriplex seeds in the salt marshes. Ducks were actively feeding around high tide, during both day and night. In the course of October the seed stock was heavily reduced due to ducks foraging, natural fall-off and wave action, whereupon the majority of the ducks left the area. The remaining ducks rested throughout daytime and flew into the adjacent hinterland at night to feed. The adjacent salt marshes of which parts are shooting zones were not used during daytime, and only irregularly at night. It is concluded that the number of wildfowl was limited by the food resources, and that switching between habitats was linked to depletion of food stocks. Shooting modified movements and caused birds to leave the area prematurely.

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Accession: 004803932

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