Official journal of the Netherlands Ornithologists' Union
|den Held J.J. (1981) Population changes in the Purple Heron in relation to drought in the wintering area. ARDEA 69 (2): 185-191|
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The population changes of the Purple Heron in The Netherlands in the period 1961-1979 were investigated. It was examined whether these changes could be caused by drought in the wintering area, West Africa. A positive correlation was found between the population size in The Netherlands and the discharges of the rivers Senegal and Niger as measures for the annual rainfall in a large part of West Africa. Moreover, it was investigated whether a similar correlation exists for the populations in southern France of four heron species that winter in West Africa. For two of these (Purple Heron and Little Egret) no correlation was found. For the Night Heron there is a distinct correlation and for the Squacco Heron it is less clear. It is concluded that the western European populations of the Purple Heron, the Night Heron and the Squacco Heron are highly dependent on the annual amount of rainfall in West Africa, but that populations oft he Little Egret are independent in this respect because of the different distribution in winter and the different habitat and diet of this species.