Red Squirrel Threats

The red squirrel faces three main threats to its survival in Scotland today:

  1. the spread of grey squirrels
  2. squirrelpox
  3. habitat fragmentation (the gradual loss of connection between areas of habitat)

Threat 1:  the spread of grey squirrels

The rapid spread of the North American grey squirrel in Britain is the main threat to red squirrel survival.  The arrival of grey squirrels in an area occupied by red squirrels causes 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 around the turn of the Twentieth Century. They are physically larger and, unlike red squirrels, 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.  This gives grey squirrels an advantage in hard winters. These differences allow grey squirrels to compete more successfully than red squirrels for food and habitat.  In areas where red and grey squirrels exist together; the presence of grey squirrels results in reduced survival rates amongst red squirrel young and reduced reproductive rates, causing the gradual 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 complete disappearance of our native red squirrels.     

Maps of red and grey squirrel distribution show how the spread of grey squirrels has resulted in the almost complete loss of red squirrels from England between 1940 and today, apart from remnant populations in northern England. 

Maps of Scotland show how the spread of grey squirrels over the last ten years alone has significantly reduced red squirrel populations, particularly in central and south-western areas; continuation of this trend would threaten the survival of red squirrels in north Scotland. 

As long as areas in north Scotland still remain grey squirrel free, Scotland is one of the only safe places left for red squirrels in Britain.  Our red squirrels account for around 75% of the entire UK population.  But grey squirrels are on the move!  We must act now to protect our remaining red squirrels.  If we do nothing, the red squirrel could become extinct on mainland Scotland.   

Threat 2:  squirrelpox

Grey squirrels can also bring another problem for red squirrels through the spread of the squirrelpox virus.  This virus, carried by grey squirrels without causing them harm, 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 eyes, nose, mouth, feet, ears and genitalia. The infected squirrel is very quickly unable to see or to feed properly and rapidly becomes malnourished. The disease is highly infectious to red squirrels 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 secretions left on feeders, dreys (the nest of a squirrel) or branches.  Squirrelpox is already present in south Scotland as grey squirrels, some carrying squirrelpox, spread northwards from England.  SSRS now incorporates Red Squirrels in South Scotland (RSSS), which is working to prevent the further spread of  the virus.  For more information, visit

If you find a red squirrel with symptoms that you think might be squirrelpox we would very much like to have the carcase post-mortemed to confirm whether the cause of death is indeed squirrelpox or something else. Please either contact one of our Project Officers or follow the instructions in this guidance note for sending the dead squirrel directly for post-mortem.

Disease surveys: Our post-mortems are carried out for us by Professor Anna Meredith, Professor of Conservation Medicine at the Exotic Animal and Wildlife Service, Royal  School of Veterinary Studies near Edinburgh. She is very keen to receive good quality red squirrel carcases for post-mortem as part of a health survey of the red squirrel population in Scotland. So even squirrels killed by cars or cats are of interest, as they may carry a range of parasites or micro-organisms that are not directly responsible for disease or fatality. Please carefully follow the advice in the post-mortem guidance note. Caution: it is not known whether any of the disease carried by red squirrels are transmissable to humans, so please handle them in accordance with the advice note.


Threat 3:  habitat fragmentation

While grey squirrel spread is the main reason for the decline in red squirrel populations in Scotland today, habitat fragmentation is also a contributing factor.

Squirrel habitat fragmentation occurs when areas of woodland and forestry become segmented and separated by development and changing land-use.  This leads to isolated areas which cannot sustain viable populations of wildlife, including red squirrels.    

SSRS aims promote improvements in habitat conditions to help red squirrels thrive to landowners by making advice on the habitat requirements of red squirrels widely available. Read more about Our Work for further details. 

Read our FAQ's to find the answers to the commonly asked questions about the red squirrel's plight and SSRS the project. 

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