FAQ: Why is the spread of grey squirrels the main threat to red squirrel survival?
While habitat loss and the squirrelpox virus have contributed to the red squirrel’s decline; 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.
Read our FAQ’s about squirrelpox and habitat loss to find out about the other factors contributing to red squirrel decline in Scotland.
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.
