Black kites wintering in Europe: estimated number, subspecies status, and behaviour of a bird wintering on Crete and Turkey

Abstract Black kites of the nominal subspecies Milvus migrans migrans breed in Europe and winter regularly in sub-Saharan Africa and the Middle East. As a new phenomenon, black kites with morphological characteristics of the subspecies Milvus migrans lineatus are observed in Europe. Based on observations of black kites in winter 2020/2021 summarized in this paper, based on other recent reports about wintering black kites in Europe and based on juvenile black kite tagged on Crete and tracked for two years, we conclude that hundreds to thousands of black kites are now regularly wintering in south of Europe, and in smaller numbers in other parts of Europe as well as in northern Africa. The growing number of wintering black kites in Europe is apparently caused by members of the population from a hybrid zone between M. m. migrans and M. m. lineatus breeding east of the Urals, i.e. from the area of the European part of Russia. This is consistent with the hypothesis of the spreading of M. m. lineatus and a subsequent hybridization zone between M. m. migrans and M. m. lineatus in a westerly direction from Siberia across continental Europe. Moreover, two black kites found dead on Crete were attributed to M. m. lineatus and M. m. migrans by cytochrome B gene sequence analyses. The juvenile black kite with lineatus features tagged on Crete and telemetrically tracked during the next two years moved to the south-western part of Russia during the next two summers, but did not breed. It spent the following two winters at the same landfill in south-western Turkey. It seems that an adaptation to food sources provided by municipal waste landfills is important for black kites wintering in Europe, the Middle East and Morocco. Highlights • Hundreds to thousands of black kites are now regularly wintering in Europe. • The growing number of wintering black kites is caused by birds from a hybrid zone between Milvus migrans migrans and M. m. lineatus in eastern Europe. • Municipal waste landfills are important as food sources for black kites wintering in Europe.