Ardea
Official journal of the Netherlands Ornithologists' Union

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Ydenberg R.C., Prins H.H.T. & van Dijk J. (1983) The post-roost gatherings of wintering Barnacle Geese: Information centres? ARDEA 71 (1): 125-131
Barnacle Geese wintering on Schiermonnikoog follow a simple routine of roosting and foraging. The morning flight from the roost usually involves a prolonged stop-over at a site en route to the foraging grounds. This 'post-roost gathering' is a centre for dispersal to and from the island. The duration of the post-roost gathering is strongly correlated with the lateness of the departure from the foraging grounds on the previous evening. The main factors promoting late departures are low temperatures and large flock sizes, both of which seem to exercise their influence by diminishing foraging opportunity for most individual geese. Flock size also shrinks as temperature declines. Temperature directly affects the rate at which the main food plants of Barnacle Geese produce new material for consumption by these birds, so low temperatures are likely correlated with low food availability. Our hypothesis is that the increase in the duration of the post-roost gathering following long days of foraging is due to the increased consideration that more geese must give to seeking other foraging sites. The post-roost gathering facilitates the accumulation of information relevant to this decision. Some methods by which information may be acquired are discussed. We emphasize the circumstantial nature of our evidence to date, but we believe that more direct test of this idea in the field can now be undertaken.


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