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Distribution and population size of pygmy owl Glaucidium passerinum in Lower Saxony, results of a countywide census 2001/2002 - with some fundamental remarks on population dynamics, DDT-contamination, origin and population development in Germany Verbreitung und Bestand des Sperlingskauzes Glaucidium passerinum in Niedersachsen Ergebnisse einer landesweiten Kartierung 2001/2002 - mit einigen grundsaetzlichen Bemerkungen zur Populationsdynamik, DDT-Kontamination, Herkunft und Bestandsentwicklung


, : Distribution and population size of pygmy owl Glaucidium passerinum in Lower Saxony, results of a countywide census 2001/2002 - with some fundamental remarks on population dynamics, DDT-contamination, origin and population development in Germany Verbreitung und Bestand des Sperlingskauzes Glaucidium passerinum in Niedersachsen Ergebnisse einer landesweiten Kartierung 2001/2002 - mit einigen grundsaetzlichen Bemerkungen zur Populationsdynamik, DDT-Kontamination, Herkunft und Bestandsentwicklung. Vogelkundliche Berichte aus Niedersachsen. Dezember; 342: 173-192

In spring 2001/2002 a county-wide census of Pygmy Owl territories was carried out in Lower Saxony. 137 territories were mapped. In consideration of the extent of census (33 - 95 %) 203 territories are calculated. 30 additional territories were taken from areas investigated in 1997 - 2000, where in spring 2001/2002 no Pygmy Owl was observed, but particularly in autumn 2002. The current total population size in Lower Saxony is estimated to 170 - 230 territories. Its about 10 % of the German population size of c. 2000 territories. The population density was 0.4 - 0.7 territories/10 km2 woodland, the highest density 1.1 - 1.3 territories/10 km2 woodland in the district of Celle. All territories were located E of the river Weser in the natural regions Lueneburger Heide (50 %), Harz Mountains (26 %), Weser - Aller - Lowland (15 %) and Weser-Leine-Highland (9 %). All territories are dependent on the presence of sprucewoods. The territories were found in Mountain - sprucewoods, in spruceforests within extensive pineforests, a few in spruce - beech - mixed woods. The breeding cavities were exclusively in holes of Great Spotted Woodpecker {Picus major) (n = 88), 97 % in sprucetrees and ever once in a pine-, birch- and asptree. The territories were located in the Lowland in 36 -150 m asl (65%), in the Highland and Harz Moutains in 300 - 500 m asl (beech range, 9 %) or in 500 - 850 m asl (26 %). In the National Park Harz the population development was in the middle constant in 1993 - 2002, but shows fluctuations until 67 %. In 1800 - 1975 there are no indications to breeding in Lower Saxony and in the other NW-Germany. In the first half of the 19th century the regions Harz Mountains and Lueneburger Heide offered no sufficient and propitious habitats to Pygmy Owl. Such habitats were in the making from 1850 until 1900. Therefore it must be assumed, that the Pygmy Owl was not breeding there in this time. The few observations in NW-Germany are distributed equal from 1875 to 1950. From 1951 to 1975 the observations are clumped in 1954, 1955, 1962, 1963, 1971 and 1976, 1977. These years coincide with years of invasions in Scandinavia and Finland, which extended to Denmark. Obviously these Pygmy Owls reached NW-Germany also. Nearly all records coincide with years of invasions. Dispersion dynamics and strategy of settlement with long distances seems to be similar to that of Tengmalms Owl Aegolius funereus, which is dependent of gradations of mice. In all probability the minimum of population size of Pygmy Owls in the hills of Central Europe from the middle of the fifties to that of the seventies was caused by the DDT-contamination similar to that of Sparrowhawk Accipiter nisus in Europe. The end of DDT-application in 1970 and a better quality of habitats in the hills of Central Europe, especially due to the beginning of "Waldsterben", have caused an increase of population density in the centres of the breeding areas in the beginning of the seventies. It follows an expansion into NW-Germany also. In Lower Saxony the Pygmy Owl breeds since the middle of seventies likely, since 1991 surely and increasing. The centres of distribution of Pygmy Owl are in the regions of Lueneburger Heide and Harz Mountains, it results above all from the low percentage of broadleaved woods and therefore from a low density of Tawny Owl Strix aluco. A menace results from the loss of living space. Therefore sprucewoods must be conserved, which are rich in cavities, structures and edges, especially old woods and trees with holes.


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