Sympatric wintering of Red Kites and Black Kites in south-east Europe

We characterized the spatiotemporal activities in winter grounds of Red Kites originated from central Europe and wintering in south-eastern Europe. We found not only Red Kites at these places but often also Black Kites Milvus migrans. Birds arrived to winter grounds in Hungary, Croatia, and Greece from 10 July to 12 December (median 22 October) and departed from winter grounds between 14 February and 22 May (median 14 March), thus staying at winter grounds from 121 to 229 days (median 145, mean 161 ± 43 SD, n = 14 cases). We usually found a number of Red Kites wintering together at winter grounds, although some Red Kites wintered alone. We found Black Kites wintering together with Red Kites at the same winter grounds in 6 out of 14 cases. The numbers of Black Kites wintering together with Red Kites were higher than the number of Red Kites at all Greek winter grounds. At winter grounds in Hungary and Croatia, the numbers of Black Kites were lower than the numbers of Red Kites or Black Kites were wholly absent. If we regarded kernel density estimate 80% (area of main foraging and roosting activities) as the best indicator as to the size of home range, we revealed that the size of a home range for birds staying at one place through the entire winter was from 10 to 108 km2 (median 72, mean 60 ± 36 SD, n = 12 cases) and that the size of home range for birds with local shift(s) in winter grounds was from 344 to 620 km2 (median 434, mean 466 ± 115 SD, n = 3 cases) which is substantially larger than the size of home ranges published to date for Red Kites wintering in central and south-western Europe.