LEBRET T (1970) Nocturnal feeding and other activities of the Grey Lag Goose Anser anser in fresh water tidal habitat in the Netherlands. LIMOSA 43 (1): 11-30.

Greylag Goose Anser anser Nocturnal feeding and other activities of Grey Lag Geese (Anser anser) in fresh water tidal habitat (Sasseplaat in the Hollands Diep) are described. This subject was studied because daylight observations were numerous, but nocturnal ones were lacking so far. The Sasseplaat is a sandbar. Its highest central parts are mud covered and have dense stands of Scirpus lacustris, Scirpus maritimus and Typha. These plants reach 2-2,50 m high. The Scirpus plants form the entire food of the Grey Lags living here. 2. Each flood tide the sandbar is covered by some 0,80 m of water. The tidal inundation lasts some 5 hours, the sandbar being exposed some 7% hours. Since the sandbar lays in the centre of a wildfowl reserve of some 9x2 km, the geese are free of disturbance. Data on the level of the sandbar, height of the vegetation, time span of coverage and exposure of the bar and other data are shown in diagram 1. 3. The numbers of Grey Lag Geese on the observation dates varied between 200 and 1200. The observations were made in 1966-1969 between September 14th and October 11th in six nights. They cover 100 hours, 70 of wich were nocturnal. The observer spent 3-4 hours per night sleeping, with many interruptions. 4. Details of the diurnal feeding and flighting habits of the geese in this locality are described. They feed especially in the first part of the ebb tide and rest at the sandy parts of the bar during low tide, often near the tidal rim. When the flood tide covers the sandbar, the geese fly towards the Scirpus fields for cover. At dusk the geese flight from open parts of the area to densely grown ones regardless of tide. 5. Nocturnal observations of the geese at close quarters in the tidal habitat were only possibly by employing an old wildfowlers practice. At high tide a schouw, a small vessel, 4m long -1,4 m wide, is hidden in the vegetation. As the tide falls, the schouw rests on the mud, until the next flood tide lifts it again. A hood on the front part of the vessel provides some cover. 6. Various calls of the Grey Lag Geese are described and related to behaviour as is done by Fischer (1965). Other noises made by the geese such as walking, flying, aggressive contacts and the cracking of Scirpus stems in the birds' bills and their puddling in the mud also helped to identify the behaviour of the geese in the dark. The frequency of their calls was registered about every five minutes. If there were many geese, the calling was continuous and the intensity of the calling was noted, though no instruments were used for this. Frequency and intensity of the calling were dependent on density and movements of the geese. 7. The observations of the 6 nights are described in detail. The distribution of feeding, flighting and periods of silence in 5 nights are shown in diagrams, the numbers of geese being too few in 1 night. It appears that the tide was the main factor governing the activities of the geese. It determines in which part of the night the geese are most active. The degree of their activity depends partly on the moonlight. Feeding is followed by a period of flighting and walking towards the tidal rim for drinking and bathing. A second period of flighting occurs about sunrise. In moonlit nights periods of silence were lacking or short. In dark nights periods of silence occurred earlier and were longer. 8. The daily rythm of the Grey Lag Geese in tidal natural habitat is different from that of Grey Lags which feed in arable or pasture land during the day and rest on water during the night. The contrast between these patterns is unlikely to be basical.

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