FAQ: Why are red squirrel populations in decline in Scotland?
Today, only around 121,000 red squirrels remain in Scotland. Habitat loss and the squirrelpox virus have contributed to the red squirrel’s decline; however the main threat to the red squirrel’s future survival is from the rapid spread of the North American grey squirrel, an invasive (non-native) species. The arrival of grey squirrels in an area occupied by red squirrels tends to cause reduced red squirrel breeding and survival rates leading to a gradual decline in their numbers.
The North American grey squirrel is an invasive (non-native) squirrel species introduced to Britain in the 19th Century. Compared with red squirrels, greys are more robust as a species due to anatomical differences. Greys are physically larger in size and, unlike reds, greys can feed on seeds with high tannin content, such as acorns, thanks to differences in digestive physiology. As a result, more food sources are available to greys and they tend to put on 20% in body weight over autumn, compared with 10% for reds. Greys also have higher juvenile survival rates. These differences allow greys to outcompete reds for food and habitat space. In areas where red and grey squirrels exist together; the presence of greys tends to result in a steady decline in red squirrel populations over time. This effect can already be seen in Scotland’s central belt where grey squirrel spread has resulted in the almost entire disappearance of our native reds there.
Grey squirrels can also bring another problem for reds through the spread of the squirrelpox virus. This virus, which is carried yet harmless to greys, is fatal to our native reds. Often mistaken for myxomatosis, the virus lodges in red squirrels’ eyelids and mucous membranes, which become infected and swollen, and produces scabs in and around the mouth, feet, ears and genitalia. The infected squirrel is unable to see or to feed comfortably and quickly becomes malnourished. The disease is highly contagious to reds and kills within 15 days of infection. Although the means of transmission is still being investigated, it is possible that the virus could be transmitted by fleas’, lice, ticks, mites, air, and urine, or by saliva left on feeders. Squirrelpox is already present in south Scotland as greys, some carrying squirrelpox, spreading from England. Red Squirrels in South Scotland (RSSS), the sister project of SSRS, is working there to contain the virus. For more information, visit the official RSSS website at www.red-squirrels.org.uk.
While grey squirrel spread is the main reason for the decline in red squirrel populations in Scotland today, habitat loss is also a contributing factor.
The project targets of SSRS aim to directly address the factors contributing to red squirrel decline. This includes working with landowners to improve habitat conditions to help red squirrels thrive and increase in number as well as working to halt the decline of red squirrel populations in key areas of north Scotland through the prevention of further grey squirrel spread. Read more about Our Work for further details.
