Boomklever Sitta europae, Drentse Vogel van het Jaar 2005
Drentse vogels , Volume 20 - Issue 1 p. 62- 75
In the first half of the 20th century Nuthatches were virtually absent in the generally treeless province of Drenthe. In 1900-50 large parts were afforested, but first breeding of the species took place in some of the few older estate-like woodlots. In 1975-80 the population in Drenthe was estimated at 8-10 breeding pairs. In 1978-93 the population had increased to 200-250 pairs (Fig. 1), occupying the larger stretches of deciduous forest. During a national breeding bird survey in!998-2000 the number of breeding pairs had firther increased to 583-726 pairs. In 2005 a volunteer-based survey covered the entire province of Drenthe. Almost all atlas squares were surveyed in 2005, a few additionally in 2006. Coverage and quality of the survey is presented in Fig. 2. The count resulted in 1935 breeding pairs, varying from 0-153 pairs per 25 km2 (Table 1). The total number of pairs is estimated to be 2030-2600 pairs. The distribution generally follows the presence of woodland (Fig. 3). Highest densities were recorded in forests with a substantial area of old deciduous trees, but coniferous forests were occupied as well. Only few patches of several square km of coniferous were devoid of Nuthatches. Estimates of the population ofNuthatch in Drenthe over several periods are given in Fig. 4. The increase matches an annual population growth of 20.5%, identical to the growth rate in the Dutch monitoring scheme for the northern Netherlands (21% annual growth. Fig. 5). During the last five or more years no population increase was noticed in areas that had been inhabited by Nuthatches since the 1970s. In an area of old oak forest in Assen no increase was noticed since 1993. Most of the increase in Drenthe was due to range expansion. We assume that the population increased by local recruitment since Nuthatches do not disperse over large distances. The fast population growth may have been facilitated by the absence of hard winters and the increase in extent and quality of new woodland habitat since the mid-20th century.
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