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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