According
to some animal rights groups the grey squirrel is a victim
of circumstance. They say it has been made
a scapegoat for
regional red squirrel population extinctions and claim that loss of the reds is
caused entirely coincidentally by habitat change. They suggest
the true facts are being hidden and scientific research being intentionally misinterpreted.
If
so, then this conspiracy must extend to British legal provisions and EU
directives both listing the grey squirrel as
an invader to be controlled, right?
Well,
no – put this argument to the test and you’ll see that the facts actually do
stack up against the grey squirrel. The reality is that, while the grey squirrel
is an important part of North American forest ecosystems, since being brought to Europe
by the Victorians in
1876, the animal has had severe ecological
and economic impacts on British
woodlands.
Acrobatic
and entertaining they may be, but the charge sheet against the grey squirrel is
based on hundreds of peer-reviewed research papers. There really is
no defence for
it.
Greys vs red in Europe
Today
there are approximately 2.5m grey squirrels in Britain, but less
than 140,000 reds. Grey squirrels out-compete native
reds for food and space. They also dig up and consume seed that red squirrels have buried as a
winter store. This behaviour reduces red squirrel skeletal growth rates and
adult size, and greatly depresses juvenile survival rates too.
In
addition, greys harbour infections – including squirrel pox, which can devastate red squirrel populations.
They elevate local viral and nematode infection rates, and bring in new
parasites, such as Strongyloides robustus, which are picked up by red
squirrels.
Occasionally
a healthy red squirrel is found with squirrel pox antibodies – some researchers
have suggested that this is evidence of them evolving
resistance to the pox. Unfortunately, 63% of
red squirrels dying from pox have also been found to have
this antibody response present and there is no evidence that
these antibodies confer immunity. Even if they did, research has also shown that
antibodies are gone within 18 months and, irrespective of any
resistance, red populations would be replaced by grey via competition
anyway.
Woodland damage
Grey
squirrels also damage and kill forest trees making it impossible for
foresters to grow high-grade hardwood. This means such material is imported
instead, bringing with it the risk of new tree pests and pathogens.
Tree
damage is most frequently seen on the branches and trunks of oak, beech and
maple; bark is stripped by squirrels eager to consume
the the sap underneath. Tree stems break or die following
stripping, which in turn leads to changes in the structure and species composition of high canopy in
amenity woodlands.
Even
songbirds are affected by grey squirrels. A recent study gave evidence of negative association
between woodland songbird fledging rates and presence of grey squirrels – though
it must be noted that this was not observed annually and only seen on some of
the sites studied. Earlier studies didn’t find evidence to indicate
greys affect bird population, but also didn’t exclude the possibility –
even for bird species whose population is increasing overall.
Other
animals may be affected by greys too: there has been some suggestion that
squirrels compete with dormice for hazel nuts, though more research is needed
to confirm the true impact.
Controlling greys
The
Wildlife Trust has recently started
to recruit 5,000 volunteers to monitor and
control grey squirrel populations. However, a look beyond the headlines will
reveal thousands of people are already legally trapping
and shooting greys across the country to control their
numbers. Volunteer groups cull 6,000 grey squirrels per year in
the north of England, for example. Even in areas where reds are absent, locals
control grey squirrels to protect woodlands or prevent damage to property. This is not some dramatic new approach by the
Wildlife Trust, but is simply reinforcing an established national
movement.
The
eradication of greys from the Welsh
isle of Anglesey saw red squirrel numbers
increase from 40 to 700 and there are other examples of
grey control halting or reversing red squirrel decline. Research has also
demonstrated that red squirrels do not prefer conifer to broadleavedhabitat and are just as happy in
either.
Future
control may involve giving the squirrels contraception,
but will almost certainly not rely solely on this because of logistical
barriers. The pine marten may assist in some landscapes
too: one Irish study found a strong negative
correlation between pine martens and greys in the woodlands studied. However,
the use of trapping and shooting will inevitably continue as part of
an integrated
national approach.
And
so the grey squirrel stands guilty as charged. Their presence has decimated the
British countryside since they were introduced from North America, and if we do
not continue to control the species, the future for red squirrels and woodland
ecosystems will be bleak. The Dawn
Chorus.
