Threats to the red squirrel

Predators, viruses, changes to landscape and the grey squirrel are pose major threats to our native red squirrel and the reasons behind a sharp decline in the UK. 

During the last century, 170 species of our native plants and animals became extinct in the UK. Although red squirrel populations are healthy on mainland Europe, the red squirrel is currently suffering major decline in the UK. Numbers in the UK have fallen from a onetime high thought to be around 3.5 million, to a current estimated population of around 150,000. The population in England is thought to be as low as 20,000. 

Historic changes in landscape use and extensive tree felling removed red squirrel habitat, but these are much less of a problem now that better controls are in place. Predation (from animals such as goshawks, buzzards, pine martens and foxes) and road deaths can impact on red squirrel populations but this is usually a localised threat. The grey squirrel is now the single biggest threat to the red squirrel in the UK.

Grey Squirrels 

Grey squirrels were first introduced to England from North America in 1876 as an ornamental species to populate the grounds of stately homes. Around 30 separate introductions occurred until 1930 when the damage caused by the grey squirrel was recognised, and it was made illegal to release a grey squirrel to the wild. Grey squirrels have rapidly dispersed and colonised much of mainland England with detriment to our native red squirrel. The illistrations below demonstrate the differences between red and grey squirrels, and click here for a red/grey ID sheet.

Grey squirrel - distinct white band around edge of tail	Red squirrel - prominent ear tufts

Greys are roughly twice as heavy as red squirrels, requiring more food. Also, greys can tolerate living in much denser populations than red squirrels in mixed and broadleaf woodlands; with greys achieving up to 15 individuals per hectare (the size of a large football pitch) and reds achieving up to 2-3 per hectare.

Grey squirrels evolved on the eastern seaboard of America in Oak and Hickory forests. As a result, they have developed a resistance to a compound called tannin which is found in seeds such as acorns. Unripe acorns are particularly rich in tannins, but are a high-energy food source. Red squirrels find tannins unpalatable, so grey squirrels can decimate crops of acorns before they ripen and become a viable food source for reds. Greys also raid caches of seeds that red squirrels have stored by burying.

The combination of grey squirrels achieving higher densities, with a higher daily food requirement, and the ability to exploit tannin-rich seeds, provides grey squirrels with a very strong ‘competitive advantage' over reds in mixed and broadleaf woodland. Failure to gain enough food prevents female reds from reproducing, and existing members of the population can gradually starve. Through the effects of competition alone, greys will replace reds well within 15 years in this habitat type.

Squirrelpox virus

However, the most significant threat associated with grey squirrels is the spread and transmission of a disease called squirrelpox virus (SQPV). It can take only one grey squirrel to introduce this virus to a local population of red squirrels, and then the virus can spread throughout the reds with devastating affect. Where a grey squirrel introduces SQPV, red squirrel population decline has been observed at between 17-25 times quicker than through competition alone.

A chance for reds

Extensive scientific research has identified one habitat type that could give red squirrels a fighting chance against the threat of grey squirrels. Conifer plantation forests can help to alleviate both the competitive and disease threats associated with grey squirrels. Seventeen red squirrel reserves have developed on this principal, and aim to protect stronghold populations of red squirrels remaining in England.