Huiszwaluwstand in Nederland in de 20ste eeuw

Population trend of breeding Common House Martin Delichon urbicum in The Netherlands in the 20th century. In 1967-‘70 the first attempt to estimate the breeding population in the Netherlands revealed 71,000-103,000 pairs. Estimates for 1973-‘77 (77,000 pairs) and !983-‘85 (25,000-50,000) were based from this estimate after adjustments according to information of a decreasing population. In 1989 monitoring was started and in 1989- 2011 every year 23,600-42,000 pairs were surveyed in 1500-2000 counting units (mainly the same squares of 2.5x2.5 km) all over the country. Relative changes were presented in indices (Figure 1). The total of 41,940 pairs in 1989-‘9I in 1987 different counting units (approximately one third of the area of the Netherlands) already was almost as big as the national estimate in 1983-‘85 and Leys & Jonkers (1991, 1992) calculated the total population of 131,000- 164,000 pairs. Comparison of counted pairs in the same area in 1967-‘70 (11,929 pairs) and 1989-‘9I (3916) show 67% decline. Based on the calculated population in 1989- ‘91 and 67% decline, the population in 1967-‘70 may amount to 400,000 to 500,000 pair. A same calculation for 1983-‘85 gave a new estimate of 100,000-200,00 pairs. These likely underestimations are supported by recalculations of populations in provinces of Drenthe, Friesland, Zuid-Holland, Zeeland and Noord-Brabant. Uncertainty among the calculation of the total Dutch population led to the publication of two estimates in the Breeding Bird Atlas of 1998-2000 (Sovon 2002). According to the approach of Leys & Jonkers (with up to 25,164 counted pairs in 20-35% of the country) the population estimated 110,000-120,000 pairs but according the calculated atlas data 70,000-145,000 pairs. However by uncertainties (likely incompleteness, coverage, biased data) the latter was downgraded to 60,000-80,000 pairs. The new atlas (2012-‘ 15) provides the opportunity to investigate differences between these calculations. Common House Martins are mainly distributed in the areas bordering Lake Ijsselmeer in the centre of the country, the Delta area in the southwest and other areas with clay soils. Elsewhere concentrations are found mainly on clay and loam soils. Breeding is con- fined to villages and buildings in farmland, breeding in cities has largely ceased. Population changes are associated with alteration of buildings and weather conditions and also (locally) to lack of mud for nest building, disturbances of nests, predation and providing artificial nests. volgehouden tellingen. Dankzij Herman Leys en Dick Jonkers en de samenwerking met Sovon/CBS hebben we de monitoring van de populatie nu goed in de vingers. Fred Hustings wordt bedankt voor zijn op- en aanmerkingen.