the grey area
Once introduced the spread of the grey squirrel across the UK was rapid, and in just 36 years the species had reached Cornwall. The native red squirrel was unable to compete for habitat and resources against the larger, invasive grey squirrel. The grey squirrel can live in densely populated areas; a hectare of woodland offers a viable habitat for up to 18 grey squirrels. Red squirrels on the other hand, live in far lower population densities of just 2 individuals per hectare. The grey squirrel spends more than three quarters of its time foraging on the woodland floor. This adaptation means that, in the autumn, grey squirrels can increase their body weight by as much as 20%, whilst reds which feed far less efficiently in broadleaved woodland, rarely manage to gain 10%. This means that in a habitat holding grey squirrels, the red squirrels rarely reach the critical mass in which they can reproduce for the following year, of course causing a huge decline of red squirrel numbers across the UK.
The decline in red squirrel population as a reaction to grey squirrels out competing red squirrels for habitat and resources was intensified by the viral infection squirrel pox (SPQV). This virus accelerated the red squirrel population decline by as much as 20 times.
“Grey squirrels are carriers of the infection and can spread the disease to red squirrels. Greys have developed immunity to the disease having been exposed to the virus for many years. In sharp contrast, the mortality rate for untreated infected red squirrels in the wild appears to be 100%, most dying within 15 days of being infected”
Northern Red Squirrels
In the 1870’s there was an estimated population of 3.5 million red squirrels in the UK, the introduction of the grey squirrel had a direct, negative impact on the red squirrel population for a number of reasons. This has resulted in a cataclysmic population decline to an estimated 120,000 individuals in the UK in 2018, 75% of which are isolated to Scotland, conservative estimates state that without human intervention the red squirrel would be extinct on the UK mainland within 20 years.
For more information on the grey squirrel and the wider detrimental effects they pose to the environment click here