IMPE J VAN (1990) Dissimilar distribution of age-classes in Brent Geese Branta branta bernicla in the southern Dutch Delta area. LIMOSA 63 (2): 41-46.

A larger fraction of juveniles was present in flocks of Brent Geese Branta branta bernicla staying on de landside of the dikes as compared to flocks staying outside the dikes in a population wintering along the southern margin of the Eastern Scheidt, province of Zeeland, The Netherlands (fig. I). This phenomenon, particularly notable at high tide, was studied in more detail during the winter of 1988/89 (tables I, 2). Flocks staying on the landside of the dikes, foraging on pastures, winter wheat and lucerne, invariably showed a higher degree of activity than flocks staying on mudflats and saltmarshes outside the dikes (fig. 2). The fraction of resting and preening birds was consistently larger in the latter. This type of spatial segregation of the age-classes (juveniles and adults) is poorly studied to date, but can very well result in considerable bias in studies of productivity of breeding seasons in the Brent Goose as conducted in various wintering areas. In the study area Brent Geese initially foraged mainly on sea lettuce outside the dikes, but this food source has all but disappeared as early in the wintering season as late November. From that moment on through the remainder of the wintering season, the rising of the tide resulted in separation of flocks with many juveniles (many families) flying inland to continue foraging there during high tide, and flocks consisting mainly of adults remaining outside the dikes and spending high tide relatively inactive there. A major cause of this phenomenon is thought to be the difference in nutritive demands (so in time and energybudgets) between juvenile and adult geese (higher demands of juveniles).

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