1. Slideshow B15: Squirrels in the UK

2. Red and Grey Squirrels Grey squirrels were introduced from America in the early 1900s. This has resulted in them becoming far more common whilst at the same time, red squirrels have become rarer.

3. Where does the grey squirrel come from? The deciduous forests of North America. The orange highlight shows the main areas where the eastern grey squirrel can be found.

4. Introduction to the UK The North American grey squirrel was deliberately introduced to the UK and other parts of Europe during the 19th century. The Victorians thought they were attractive and so brought them into the country. Since then it has thrived in parks, gardens and woodlands.

5. Grey squirrel vs. Red squirrel Grey squirrels can weigh as much as 600 grams, twice that of an adult red squirrel. Grey Squirrels live for an average of 7–9 years, compared to 6–8 years for reds. This gives the grey squirrels advantages over the red squirrel.

6. Grey squirrels also have some behavioral advantages over reds. The red squirrel lives mainly in the trees. It spends only 33% of its time on the ground. The grey squirrel spends up to 80% of its time foraging on the woodland floor. This means that in the autumn grey squirrels can increase their body weight by as much as 20%. The reds rarely manage to gain 10%.

7. Disease between the species In 1984 a squirrel was found to be infected with a disease that was identified as a parapoxvirus. This disease is fatal to red squirrels, but it is carried by the grey squirrel.

8. Economic impact of the grey squirrel Grey squirrels cause damage to trees by bark-stripping. This results in the death of 5% of trees. In 2000 it was estimated that squirrel damage reduced the value of commercially grown trees in the UK by £10 million.

9. Ecological impact Grey squirrels are partly responsible for the decline in many bird species. They eat the bird eggs or the chicks. They also take over nest sites and eat food such as seeds and nuts which would otherwise be eaten by birds.

10. Management practices Control measures are governed by strict legal guidelines, but permission can be obtained to shoot, trap or poison grey squirrels. The Forestry Commission currently spends £200,000 per year controlling grey squirrels. They estimate that a great deal more would have to be spent for their impact on British wildlife to be reversed.

11. Questions 1What could be causing the decrease in numbers of red squirrels? 2What resources are both squirrels after? 3What is the term used to describe organisms being after the same resources?