RINGING RECOVERIES AND THE INCREASE IN NUMBERS OF EUROPEAN GREAT CRESTED GREBES PODICEPS CRISTATUS

221 recovery data of European Great Crested Grebes were analysed. Grea t Crested Grebes migrate SE to winter mainly in southern parts of the (former) Soviet Union or Turkey (Fennoscandian birds), or in the centr al European lakes (individuals from northwestern Europe). A second win tering area is found to the SW, along the southern North Sea coasts. T he proportion of Dutch grebes recovered in winter within The Netherlan ds increased significantly over the last decades. Field counts show th at also the absolute number of moulting and wintering grebes in The Ne therlands 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 i n the genetic composition of the Dutch breeding population. This presu med evolutionary change would have been caused by extensive man-made c hanges to the habitat (large areas of newly created lakes) together wi th a strong selective advantage for locally overwintering individuals.