Der Rotmilan (Milvus milvus) im Unteren Eichsfeld.
The Red Kite (Milvus milvus) in Lower Eichsfeld.
by Nicole Wasmund
Date of Examination:2013-09-23
Date of issue:2013-11-19
Advisor:Prof. Dr. Michael Mühlenberg
Referee:Prof. Dr. Michael Mühlenberg
Referee:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Sigrid Hoyer-Fender
Referee:Prof. Dr. Christoph Kleinn
Referee:PD Dr. Mark Maraun
Referee:Prof. Dr. Heiner Flessa
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EnglishIn the present study were examined population density, habitat use and composition, young bird rearing, food and predation on Red Kite (Milvus milvus). Essential questions were how stable is the stock in the area and what causes could there be for the decrease previously suspected. In essence, the hypothesis was tested that the lack of food is the essential component that caused the Germany-wide decline of red kites since 1990 (NICOLAI/ MAMMEN 2009). Study area was the bird sanctuary EU SPA V19 (Unteres Eichsfeld) with an area of 13,710 hectares. The study period lasted from 2009 until 2012. To determine the population density in the bird sanctuary data from 2003 and 2008, and obtained data from the four study years were used. The mean value of the years 2003 to 2012 were 12.2 BP/100 km2. The hypothesis that the existence of the red kite has deteriorated in the study area could not be confirmed. Even the reproduction values changed since 2008. Despite a short-term positive development, reproduction rates (breeding success) are yet under the Germany-wide average of 1.68 JV / BP (if not entirely comparable methodology of the acquisition). The previous mapping data have not been and is not sufficient to predict long-term population trends. To determine the use of the open land and settlement area, red kites were observed from 2010 to 2012 and the foraging search flight times were recorded. It was observed landscape sections, localities, waste management facilities and grassland during and after mowing. By far the most common mowing was used during processing and a few days later. The search flight times during the mowing were present significantly higher than after mowing. Mainly grassland, which was mowed by “Flächenmahd”, was searched for food. Alfalfa was in a year, regardless of mowing regime, compared with normal grassland preferred. The landscape sections were different frequented. Cereal and canola were avoided relative to their area of interest (2010 and 2012 significant). Grassland, however, was preferred in each year (2010 and 2012 highly significant). Also maize (in May and June), water and beet areas were preferred. This can be an avoidance of densely vegetated areas identify where the Red Kites can not hunt prey. The villages were intensively searched for food, than the surrounding landscape. The disposal facilities, that were investigated in 2011, could only be used to search for food when the red kites was given the opportunity to fly into them. Otherwise, they played no major role. To determine the proportions of grassland in the potential used areas around the nests from red kites, all grassland areas were digitized in a buffer of 3 km around the nest. The shares in the open land areas were between 8.65% and 17.40% and were partially above and below the proportion of grassland in the study area of 11%. 2011 and 2012, at 68 places carcass was laid out and at these places camera traps were used to document red kites. Most of the birds, which used this kind of food, were corvids, red kites and buzzards, which arrived with only small intervals on the carcass. 35 % of the carcass were used by the red kites. To prove or disprove the hypothesis of lack of food during the breeding season, 12 nests of red kite, a buzzard nest (Buteo buteo) and a black kite nest (Milvus migrans) were filmed between 2009 and 2012 and documented the young bird rearing, food and the food supply. The red kites had a total of 27 young birds, of which only 19 were fledged. 8 young birds were killed by goshawks (Accipiter gentilis). The buzzards successfully raised two young birds and the black kites 3 young birds. In the analysis of food the weight of the various components of the diet could be quantitatively specified. The food at the red kite nests was mainly composed of three components: carrion, mammals (including small mammals) and songbirds. Differences were observed between individual pairs of red kite, between years and between the three raptor species. The years 2010 and 2012 differed significantly at the nests of red kite by the higher proportion of fed small mammals, from the years 2009 and 2011. In years with fewer small mammals (2009, 2011), however, more carrion was fed. The buzzards fed most small mammals and only insignificant amounts of carrion birds and songbirds. Contrast, amphibians play a more significant role. The black kites fed mainly carrion, small mammals and songbirds. Striking was the high proportion of earthworms in some nests of red kite and the nests of black kite. Starving young birds were observed in no nest. 8 of 12 pairs of red kite fed daily average of 150g of food per young bird. The expected total weight, however, was reached by 9 pairs of red kite. The pairs with two young birds fed the young birds better than pairs with three young birds. The hypothesis that there is lack of food during the breeding season, can not be confirmed based on the results obtained. Indirect food shortages may adversely affect foraging by long flights of adult birds and when they stay away for long time from the nest. The observed predation by goshawks supports this thesis. Also to determine the mammalian predation risk by raccoon and marten, nest trees were equipped with camera traps and photographed potential predators. At 4 of 9 nests climbing raccoons and at 1 of the 9 nests a climbing marten could be photographed. 3 of the broods were abandoned. Whether this was caused by the presence of predatory mammals, could not be said and needs larger samples in the future. The study was able to show how diverse the food of the red kite can be in different years. So small mammals play, especially in years in which they occur frequently, a greater role. The grassland areas have been preferred to the other surface types in all years, and especially the mowing. The results highlight the importance of a richly textured, open cultural landscape for the red kites, particularly during the breeding season.
Keywords: red kite, black kite, mowing, lack of food, buzzard, racoon, predatiom
Schlagwörter: Rotmilan, Schwarzmilan, Nahrungsmangel, Prädation, Waschbär, Bussard