Why Are Red Squirrels Declining in the UK? Causes Explained

How far have red squirrels declined?

A century and a half ago, the red squirrel lived in woodlands across Britain and Ireland. Today it has vanished from most of England and Wales. In England, wild red squirrels remain mainly in Northumberland, Cumbria and parts of Yorkshire and Merseyside, plus the Isle of Wight and Brownsea Island. Scotland holds the majority of the population.

Estimates of red squirrels left in Britain vary from about 140,000 to roughly 290,000, depending on the survey and method. That compares with roughly 2.7 million gray squirrels. Globally the red squirrel is listed as Least Concern, but the Mammal Society’s 2020 Red List for Britain’s mammals classed it as Endangered in Great Britain.

Cause 1: competition from gray squirrels

The eastern gray squirrel is larger and heavier than the red, at about 400–600 g (14–21 oz) against 250–340 g (9–12 oz). The two species never need to fight. Instead, grays simply do better in most British woods:

• Acorns. Gray squirrels can digest acorns despite their bitter tannins. Red squirrels get far less nutrition from them, so in oak-rich woods grays have a large food advantage.
• Food theft. Grays find and eat the seeds and nuts that red squirrels bury in autumn for the lean months of late winter and spring.
• Higher numbers. In broadleaf woodland, gray squirrels typically live at several times the density of reds.
• Breeding. Where grays are present, female red squirrels tend to be lighter and raise fewer young, so red numbers slowly fall even without disease.

In many broadleaf and mixed woods, competition alone has replaced reds with grays within about 15–20 years of the grays arriving. Red squirrels hold out longer in large conifer forests, where small conifer seeds suit them better than grays.

Cause 2: squirrelpox

The second, faster killer is squirrelpox virus. Many gray squirrels in Britain carry antibodies, showing they have met the virus, but they rarely get sick. They can pass it to red squirrels, probably through shared feeding places and contact. In reds, the disease causes ulcers and scabs around the eyes, mouth, feet and genitals, and most infected animals die within about two weeks.

Where squirrelpox arrives, red squirrels can disappear many times faster than through competition alone. In 2007–2008, an outbreak at Formby in Merseyside killed around 80% of the local reds, though the population later recovered. Some red squirrels have survived infection, and researchers are studying whether resistance could develop.

Cause 3: habitat loss and fragmentation

Red squirrels need large, connected woods with a reliable supply of tree seeds. Britain lost most of its native forest centuries ago, and much of what remains is broken into small, isolated patches separated by farmland, roads and towns. Small populations in isolated woods are easily wiped out by a bad seed year, disease or the arrival of grays, and cannot be recolonized from elsewhere.

This is not a new problem. By the 18th century, red squirrels had become very rare in much of Scotland after widespread forest clearance, and they recovered only after new forests were planted and squirrels were reintroduced from England and Scandinavia.

Other pressures

• Traffic. Road deaths are a significant cause of loss in some populations, especially in autumn when squirrels travel more.
• Predators. Domestic cats, foxes, birds of prey and stoats take red squirrels, and cats can be a major threat near houses.
• Other diseases. Adenovirus and other infections also kill some red squirrels.
• Food shortages. Years with poor seed crops cause high death rates, particularly among young squirrels.

How red squirrels are being helped

Conservation in the UK combines several approaches:

• Keeping grays out of strongholds. Groups such as Saving Scotland’s Red Squirrels and Red Squirrels Northern England work to stop gray squirrels from spreading into key red areas. Releasing gray squirrels into the wild is illegal under the Wildlife and Countryside Act 1981.
• Islands as refuges. On Anglesey, gray squirrels were removed from 1998 and red squirrels were reintroduced; the island now has the largest red population in Wales. Brownsea Island and the Isle of Wight have never been colonized by grays.
• Forest management. Some large conifer forests, such as Kielder in Northumberland, are managed as red squirrel strongholds, with tree species chosen to favor reds.
• Fertility control research. Scientists are developing an oral contraceptive for gray squirrels, delivered through feeders that only the heavier grays can open, as a humane long-term option.

The pine marten effect

One of the most hopeful discoveries involves the pine marten, a native tree-climbing predator related to weasels that is recovering in Scotland and Ireland. Studies in Ireland and Scotland found that where martens returned, gray squirrels declined sharply and red squirrels increased.

Researchers think gray squirrels are more vulnerable because they spend more time on the ground, are heavier on thin branches and did not evolve alongside martens, so they react less effectively to them. Red squirrels, which share their native forests with martens across Europe, are better at avoiding them. Pine martens have also been released in Wales and are being considered for more parts of England.

Is there hope for red squirrels?

Red squirrels are now stable or recovering in some areas, including parts of Scotland and on Anglesey. Their long-term future in Britain depends on keeping gray squirrels and squirrelpox out of key areas, protecting and connecting woodland, and the spread of predators like the pine marten. For more on how the grays arrived, read why are gray squirrels invasive in the UK?, and to tell the two apart, see red squirrel vs gray squirrel.