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Thrush and
anvil |
01.06.2002
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Ó
Robert Burton |
Song thrushes are famous for eating
snails. They bash the shells against a stone (marked with a
red line above) and extract the battered and bruised body of
the poor snail. But are they really a ‘gardener’s
friend’ for keeping these pests at bay? I pondered this
when I found a thrush’s anvil while working in the garden.
The anvil was only a 2-inch pebble but it was surrounded by
the broken remains of a dozen shells, mostly of the banded
snail but one of a large garden snail.
A dozen snails is nothing compared to the numbers I find
crawling over my patio after dark or hiding under flowerpots
and piles of bricks. The truth is that thrushes eat snails
mostly during two periods in the year: in mid-summer and
late winter. This is when other animal foods can be in short
supply because they are sheltering from drought or hidden by
snow. A snail’s shell is not a complete protection but it
is much more economical for a thrush to gobble a caterpillar
or worm than to go through the palaver of carrying a snail
to an anvil, laboriously smashing the shell and extracting
the contents. Snails can be regarded as a form of emergency
ration.
For this reason, I cannot imagine that the two
pairs of thrushes that frequent my garden have any impact on
the numbers of snails. The moral is that it is dangerous to
conclude that the presence of a predator necessarily has a
serious effect on its prey.
This works both ways. Song thrushes are thriving in
my garden despite regular visits from magpies, crows, jays,
cats and sparrowhawks.
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