OOSTERHUIS R (2020) Dramatic decline of Eurasian Tree Sparrow Passer montanus in Groningen, the Netherlands. LIMOSA 93 (1): 28-30.
From 2010 onwards I counted the number of Tree Sparrows
on two feeding spots in gardens in the villages of Leek
and Lettelbert (Table 1), which were also visited by House
Sparrows. I tallied bird numbers from pictures made by
motion detection cameras.
By means of colour marked House Sparrows, I was able to
estimate the yearly number of sparrows visiting the feeding
spots. House Sparrow populations amounted to 179-207
individuals in Leek and 83-111 individuals in Lettelbert,
without any apparent trend (Fig. 1). The proportion of Tree
Sparrows in Leek decreased from 5.6% in the winter of
2010/11 to 0.03% in 2018/19. In Lettelbert the proportion
declined from 9.2% in 2010/11 to 0.16% in 2018/19 (Fig. 1). The
annual decrease for Leek was 44%, for Lettelbert 47%.
As during the study period House Sparrow numbers
remained stable, I assume the decline in proportion of
Tree Sparrows reflects a population decline. Despite major
differences in land use between Leek and Lettelbert (Tab. 1),
the decline progressed at the same dramatic rate. Feeding
ad libitum obviously could not prevent these Tree Sparrow
populations from collapse.
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