NOCTURNAL FEEDING IN MOLTING GREYLAG GEESE ANSER-ANSER - AN ANTIPREDATOR RESPONSE

The diurnal activity patterns of Greylag Geese were studied at a Danis h moulting site. Before moulting, Greylag Geese foraged throughout the 24 hour period, but changed to nocturnal feeding behaviour exclusivel y and roosted on offshore islets during the day, as they became flight less. As the moult progressed, geese preferred to feed in coastal habi tats and responded more strongly to predator-like stimuli, such as ove rflying herons and helicopters, even though real predators were absent . This increased susceptability to commonplace events may be a respons e to their restricted mobility and ability to escape potential predato rs during moult. Since the frequency of the predator-like stimuli was lowest at night, we suggest that moulting Greylag Geese compensate for their lowered tolerance threshold to predator-like stimuli by feeding at night when the probability of being disturbed is less. Alternative nutrition-related hypotheses of nocturnal feeding are discussed, howe ver these could not explain the observed changes in feeding behaviour, when Greylag Geese became flightless.