Nocturnal feeding in moulting Greylag Geese Anser anser- An anti-predator response?

The diurnal activity patterns of Greylag Geese were studied at a Danish moulting site. Before moulting, Greylag Geese foraged throughout the 24 hour period, but changed to nocturnal feeding behaviour exclusively and roosted on offshore islets during the day, as they became flightless. As the moult progressed, geese preferred to feed in coastal habitats and responded more strongly to predator-like stimuli, such as overflying herons and helicopters, even though real predators were absent. This increased susceptibility to commonplace events may be a response to their restricted mobility and ability to escape potential predators 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, however these could not explain the observed changes in feeding behaviour, when Greylag Geese became flightless.

Kahlert J., Fox A.D. & Ettrup H., ARDEA 84 (1): 15-22.