Natal dispersal in Black Kites Milvus migrans migrans in Europe

Abstract

The European population of Black Kites of the nominate subspecies Milvus migrans migrans (Boddaert, 1783) is estimated at 81,200–109,000 pairs. The birds winter in Africa but their natal dispersal remains largely unstudied. Here, we analyze the behavior of 25 GPS-tracked Black Kites tagged from 2014 until 2018 using GPS/GSM telemetry devices from 16 nests in Bulgaria, Czech Republic, Germany and Slovakia. We calculated juvenile Black Kite post-fledging areas (PFA) using Kernel density estimations 95% (KDE95) and minimum convex polygons 95% (MCP95). Our results revealed that the average occupied PFA for juvenile birds was 2.8 km2 (range 0.006–20.1 km2) as KDE95 and 0.3 km2 (range 0.07–1.35 km2) as MCP95. Birds left PFA from 29 July to 30 August (median 12 August). Two main migration routes were used by tagged birds, namely a southwestern European route crossing the Strait of Gibraltar and a southeastern European route to Turkey and the Middle East. Migration routes which directly crossed the Mediterranean Sea to Africa from Italy and Greece were rarely used. Winter quarters were located in sub-Saharan Africa throughout the belt from Senegal and Gambia to Ethiopia. Four Black Kites remained to stay in tropical Africa during their first summer, seven birds moved north but to substantially lower altitudes (in Morocco, Spain and Turkey) then those in their natal areas. During the second year, Black Kites wintered again in the tropical part of sub-Saharan Africa, summer quarters were located north from the winter quarters, three birds stayed throughout the summer in Africa, three in south to central Europe, one in Turkey and one in northwestern Russia. One 3-year-old bird (fourth calendar year) attempted to nest but it was unsuccessful and occurred 15.6 km from the natal nest. Temporary settlement areas (TSA) were commonly used by Black Kites during migratory routes, winter and summer quarters. The average home range size of TSA was 233.8 km2 (range 0.99–852 km2) as KDE95 and 140.2 km2 (range 0.1–1054 km2) as MCP95. As usual, siblings used the same migratory routes and also shared the same winter and summer quarters. Our findings suggest that the genetic background of the migration behavior of Black Kites is strong.