The Changing Colours of British Squirrels

As we head into autumn and the leaves fade from green to orange, now is the perfect time to discuss another change of colour. Our squirrels!

Image Credits: Charles J Sharp

In my garden, grey squirrels are a staple of the autumn season. I watch them scamper up trees and poke their heads into flowerpots, run about on the lawn and occasionally flee next door’s cat. It’s difficult to imagine my garden without them. But the truth is grey squirrels had a long way to travel in order to end up where they are today. In 1876, Victorian banker Thomas Brocklehurst brought home a pair of grey squirrels as a novelty from a business trip to America.

Compared to the native British red squirrels these new arrivals were stockier and stronger, and crucially, both species of squirrels shared similar diets and favoured similar habitats. This meant Thomas Brocklehurst had inadvertently created a deadly inter-species competition that still remains today.

Invasive species are organisms which are non-native to an area and have harmful effects. Having a multitude of species in itself is usually a benefit, providing biodiversity and diversifying food webs in a habitat. However, the issue with invasive species is not in their inherent existence but is how they have been transplanted into an environment which is not adapted to them. Most invasive species are perfectly harmless in their native area. This is because a native ecosystem evolves and balances to reach stability, every species has its ecological niche with relatively stable food webs and predator-prey relations. Unfortunately, grey squirrels are outcompeting red squirrels and are now the dominant squirrel species in Britain.

Grey squirrels are estimated to cause over £17 million worth of damage in the UK. While both red and grey species can be highly destructive in forests as they strip tree bark to gorge themselves on the sap underneath, grey squirrels do this more often and for a longer time period in the year than red squirrels. 

Image credit: Alexas Fotos via Pixabay

When a species is transplanted to a foreign ecosystem, this disrupts the existing environment. In the case of the grey squirrels, they also carry ‘squirrel pox’, a virus that causes ulcers, lesions and death to red squirrels while leaving their grey counterparts unharmed. Not as nice and fluffy as they seem! As a result of these grey invaders, red squirrels are now only found rarely in parts of Northern England and Scotland

The war on grey squirrels is only set to increase, with red squirrels being able to claim many high profile individuals among their supporters such as Prince Charles. It is currently illegal to release grey squirrels under the Invasive Alien Species (Enforcement and Permitting) Order with sanctuaries being forced to cull any in their care.

However culling still meets with fierce opposition, such as this petition protesting against The Wildlife Trusts’ volunteer drive to recruit people to kill grey squirrels. Elsewhere in Italy, grey squirrel management has taken place through sterilisation and release which prevents them from reproducing. One other proposed solution includes this delightful fellow…

Image credits: Eric Johnston

…meet the pine marten! This wonderful furry creature treats grey squirrels as a tasty snack and could help keep numbers down. Introducing predators to manage our vastly growing grey squirrel population is heralded as one of the most effective methods of control and carries the additional bonus of less ethical issues about human involvement through direct hunting.

Unfortunately the pine marten itself has had experience of being hunted throughout the 1800s for their fur and as a result, pine martens are the focus of many conservation projects to boost numbers. Currently pine martens are predominantly found in Scotland with fragmented populations in the rest of the UK.

Before we can even consider using pine martens as a grey squirrel control, we need to ensure there are large and stable pine martens populations to start with. Additionally, while studies show that pine martens reduce grey squirrel populations and encourage reds, it is also known that pine martens tend to avoid urban areas.

This means any progress in reducing grey squirrel numbers in rural areas is likely to be cancelled out by migration from those in the city. There is also evidence that pine martens do actually target red squirrels as well as greys, and the reason why they are perceived to eat more grey squirrels is simply because there is a higher abundance of grey squirrels around. Further research and testing of methods must be carried out to create a cohesive management plan for the future.

But for now, grey squirrels are here to stay! The complex relations between predator and prey are not linear and it is important to note that interfering with an ecosystem may have far reaching and unexpected effects. Thus, grey squirrel management is still full of uncertainty. The only thing we know for sure is that it will take many autumns for our squirrels to change colour again.

About the Author: Amy Leung is a first year geography student at Oxford University who thinks the world would be better with more trees.

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