Inventarisatie van de Rode Wouw Milvus milvus als broedvogel in Drenthe en Friesland in 2019

Throughout SW-Drenthe, N-Drenthe (Drentsche Aa) and SE-Friesland the presence of Red Kites was investigated during March-October. One successful nest was found in De Wijk. On 9 June three nestlings were ringed; the two oldest were equipped with a transmitter. Laying date of the first egg was back calculated (maximum wing chord of the oldest chick) at 7 April, with hatching date estimated at 17 May. Observations on 16, 23, 28 and 30 July during 14.5 h in the morning showed that adults arrived with food 14 times, on average once per 62 minutes. The oldest young left the nesting site on 26 July (77 days of age), the second oldest on 4 August. According to GPS-transmitter data, the greatest flight distance of the two young on average was 99.8 m (sd 43.6) per day between 10 June and 2 July; this increased to 270.1 m (sd 273.2) between 4 and 26 July. A nest visit of observers on 3 July coincided with longer flights of the young, i.e. 233 and 798 m respectively. Except for 3 July (the day with disturbance at the nest site), the two young roosted at the nesting place until 26 July. After leaving the nest site the young dispersed across north-eastern Netherlands and north-western Germany. The oldest young stayed 55 days near Hannover (224 km from natal site) and the second oldest 18 and 25 days near Bremerhaven and Oldenburg respectively (202 km from natal site). Mainly in October both young travelled south to the regions of Rhine, Ruhr and Ardennes and in November across France to the wintering area in northwestern Spain. Plucks, prey remains and pellets collected at the nest site contained the remains of at least 26 different vertebrate species. Birds represented 50% in numbers, mammals 46%. Observations of moulting breeding birds and collection of moulted primaries (2 to 10, counted descendantly, n=12), secondaries (1 to 3 and 11/12, counted ascendantly, n=6) and tail feathers (1 to 6, n=7) showed that primary moult took place between early May and mid-September whereas rectrices were moulted between mid-July and early September. These observations indicate a complete moult of primaries and rectrices in the breeding area, with the male's moult ahead of that of the female. Intensive fieldwork to locate territorial and nesting Red Kites in April-September yielded two more territories in the basin of the Drentsche Aa (mid and south) and two in SE-Friesland (basin of Tjonger and Linde). Elsewhere in Drenthe and Friesland no territories of Red Kites were located. In Drentsche Aa and SE-Friesland Red Kites were individually distinguished on the basis of behaviour, plumage and moult. In addition to the potential breeding birds, often present as duos, at least 13 other individuals (4 adults, 8 2nd calender-year kites and one age unknown) were identified, Intensive fieldwork to locate territorial and nesting Red Kites in April-September yielded two more territories in the basin of the Drentsche Aa (mid and south) and two in SE-Friesland (basin of Tjonger and Linde). Elsewhere in Drenthe and Friesland no territories of Red Kites were located. In Drentsche Aa and SE-Friesland Red Kites were individually distinguished on the basis of behaviour, plumage and moult. In addition to the potential breeding birds, often present as duos, at least 13 other individuals (4 adults, 8 2nd calender-year kites and one age unknown) were identified, probably floaters or migrants. Breeding could not be demonstrated, but broods may have failed early in the breeding cycle. The number of sightings in June July showed a striking decline.