Northumberland is a major stronghold for red squirrels, in particular Kielder forest, which is the largest red squirrel reserve in England. Monitoring programmes conducted in 2024 by Red Squirrels Northern England (RSNE) have shown red squirrel occupancy at Kielder reserve was the highest recorded since the programmes beginning in 2012; finding sightings in over 60% of survey sites.
The grey squirrel (Sciurus carolinensis), imported from North America during the Victorian period, is considered one of the biggest threats to red squirrel populations. They have many competitive advantages, one being the ability to digest tannins, allowing them to eat seeds and nuts before fully ripened.
Red squirrels are ecosystem engineers that act as seed dispersers for pine forest regeneration. They also spread mycorrhizal fungi spores, that help maintain healthy trees through a symbiotic relationship. Although the impact of grey squirrels is still significant on woodland regeneration, they also cause damage through bark stripping when in high densities. Research has identified it is likely that they can digest calcium from the tree bark due to the presence of oxalate degrading bacteria in their gut, which could be an explanation for the bark stripping.
Squirrel pox virus (SQPV) is one of the leading threats to UK red squirrel populations. It is carried asymptomatically and transmitted by grey squirrels. A high prevalence of SQPV antibodies in grey squirrels and an absence in red squirrels has been detected, indicating grey squirrels have gained a natural immunity. The virus presents in lesions, ulcers and lethargy and has an extremely high mortality rate. It is mostly transferred through bodily fluids and shared parasites in areas of co-habitation. The effect of an outbreak can be catastrophic for population numbers as seen in Formby (2007/8), where an estimated 80% of their red squirrels were lost.
Grey squirrels aren’t the only cause for the decline in red squirrel populations, with 61% of red squirrel mortality being related to human activity.
Grey squirrels aren’t the only cause for the decline in red squirrel populations, with 61% of red squirrel mortality being related to human activity. The loss of Britains expansive woodland’s, which is the preferred habitat of red squirrels is also a major contributing factor. Whereas grey squirrels are more able to adapt to fragmented habitat’s.
Conservation projects promoting the natural recovery of pine martins and raptors, which predate on grey squirrels are ongoing across Northumberland, offering hope for red squirrels through a more balanced ecosystem.