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VAN MANEN W (2020) House Sparrow Passer domesticus and Tree Sparrow P. montana in the Netherlands, 42 years of monitoring. LIMOSA 93 (2): 49-58.

Winter point counts (PTT) have been conducted in the Netherlands since 1978. Observers were free to choose 20 observation points along a fixed route and counted each point once per year between 15 December and 1 January. All birds, irrespective of the distance from the observer, were counted during five minutes. Number of observation points increased from 1100 – 3280 in 1978-82, to 6000 – 10 000 in 1983-2015, and around 12 000 in 2016-19. Habitat characteristics at the observation points were characterised by the observers themselves (cf. Fig. 7).
In 1978-2019 the number of House Sparrows decreased at an annual rate of 1.8%, whereas Tree Sparrows decreased at a rate of 5.0% (Fig.1). For House Sparrows the mean number of birds during a point count (excluding observation points where no House Sparrows were seen) decreased at a similar rate, which means that the distribution and numbers declined in parallel (Fig. 2). For Tree Sparrows, the mean number of birds at non-zero points initially increased, before it decreased during the nineties. This means that the Tree Sparrow started to retract in range before numbers dwindled. Groups of more than 100 Tree Sparrows occurred 2.3 times per year in the eighties, 2.3 times in the nineties, 1.5 times in 2000-2009 and 0.5 times/year in 2010-19. Strong fluctuations in both numbers (Fig. 1) did not correlate with weather (such as winter and summer indexes and precipitation).
Trends of House and Tree Sparrow differed between regions and soil types (Fig. 3-6). Declines were strongest in the south, and for sandy soils. Differential declines between regions and soil types reduced initial differences in numbers between areas. House Sparrows showed a strong preference for urban areas (Fig. 7), whereas Tree Sparrows were most abundant on farmland. House Sparrows declined strongest at points with the highest proportions of urban areas (Fig. 8). Likely causes for the declines of House and Tree Sparrow include the more intensive use of space in human settlements, including gardens, parks and other public spaces, and the intensification of farming practises such as growing silage maize instead of oat and rye, increased use of pesticides, and the disappearance of mixed farming. For Tree Sparrows climate change could also play a role. It is not likely that predation by Sparrowhawks Accipiter nisus, a species that strongly increased after the ban on persistent pesticides in the seventies, plays a role in the decrease of sparrows. Since the nineties, Sparrowhawks themselves are in decline, which did not lead to the recovery of sparrow populations.

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limosa 93.2 2020
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