NATURA

Image 18. Grey squirrel Sciurus carolinensis in Attenborough Nature Reserve,
Nottingham.
The Grey squirrel Sciurus carolinensis is a common mammal
in the UK. It was introduced to the UK from North
America during the late 19th century and is now all over
England and Wales and in variable habitats. Their success
compared to the native Red squirrel Sciurus vulgaris is both
because of their ability to get food and prepare for the
winter, and because of a virus that they brought with them
and the red one got infected by (the grey one is resistant
to it). When walking in parks or just in the streets, Grey
squirrels can often be spotted. They are more active during
the summer when gathering food on the ground, running
around fields or up tree trunks.
Image 19. Brown rats Rattus norvegicus in Attenborough Nature Reserve, Nottingham.
There are two species of rats in the UK, the Black rat
Rattus rattus and the larger, more numerous Brown
rat Rattus norvegicus. Neither of them is native. They
arrived on shores as stowaways from Asia, and have
spread around. The general judgment is that rats are a
plague and a lot is done to discard them. That is mainly
due to the belief that rats can spread diseases like the
epidemic Black Death, as well as the great plague of
London that occurred in the 17th century.
Rats are rodents, they can destroy things with their
teeth and they eat a lot. They are an example of species
that has adapted and succeeded extremely well in urban
environments. People do their best to control their
population. One way is to intoxicate them, but research
show that rats have evolved a great resistance to poison
so often that method does not work. An effective way
that seems to work is to limit the source of food available
for rats. We often evaluate species from our point of
view, forgetting that other species can benefit from rats.
Some birds feed on rats so their success is not bad for
all.
The common hedgehog Erinaceus europaeus is more welcome
in urban areas than rats. Hedgehogs are considered
harmless and even useful as they eat many garden
pests. They are common in fields, hedgerows, woods
and in gardens. They can normally be seen during the
warmer months and they are mostly active at dusk and
at night.
Unfortunately, the hedgehog population in Britain is
declining. Most surveys attain the same conclusion that
about a quarter of the hedgehog population has been
lost in the last ten years. The reason is not known for
sure, but possible reasons are changes in agriculture
leading to changes in habitats and use of pesticides to
reduce their prey stocks (invertebrates and small vertebrates).
Other explanations include smaller and tidier
gardes often closed with fences that the hedgehogs
cannot get through. In addition to this, the cities are
getting bigger leading to more isolated populations of
hedgehogs. Furthermore, a lot of animals get killed on
the roads trying to get between places.
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