Ringing recoveries and the increase in numbers of European Great Crested Grebes Podiceps cristatus.

221 recovery data of European Great Crested Grebes were analysed. Great Crested Grebes migrate SE to winter mainly in southern parts of the (former) Soviet Union or Turkey (Fennoscandian birds), or in the central European lakes (individuals from northwestern Europe). A second wintering area is found to the SW, along the southern North Sea coasts. The proportion of Dutch grebes recovered in winter within The Netherlands increased significantly over the last decades. Field counts show that also the absolute number of moulting and wintering grebes in The Netherlands increased dramatically since the sixties, whereas the total number of grebes wintering in Switzerland decreased. This increase in local wintering may be one of the causes of the important increase in the breeding population since the seventies. Although not enough data are available, the results suggest that the increase in the proportion of locally wintering Dutch Great Crested Grebes may reflect changes in the genetic composition of the Dutch breeding population. This presumed evolutionary change would have been caused by extensive man-made changes to the habitat (large areas of newly created lakes) together with a strong selective advantage for locally overwintering individuals.

Adriaensen F., Ulenaers P. & Dhondt A.A., ARDEA 81 (2): 59-70.