Red and grey squirrels

Red and grey squirrel diet and energy needs

Red and grey squirrels eat the same types of tree seed including oak acorns. Interestingly, dietary studies have revealed that grey squirrels are better able to extract the proteins and energy stored in acorns than are red squirrels. Where oak is present in a landscape it therefore gives grey squirrels a competitive advantage. Grey squirrels are almost twice the weight of red squirrels and consequently require more energy per day. In upland spruce forests where tree seeds are so small that grey squirrels find it difficult to eat enough to satisfy their basic energy needs the smaller red squirrel is better able to survive.  These respective facts help explain why regionally where grey squirrels are present, red squirrels persist for longest in coniferous stands.

Did you know?

By limiting the amount of oak in conifer forests, conservationists are able to make the habitat less attractive to grey squirrels. RSST are supporting the development of forest plans that help safeguard red squirrels.

The impact of grey squirrels up red squirrel populations

Research has shown that when grey squirrels start to colonise broadleaved woodlands, adult red squirrel survival rates are unaffected and there is little evidence of frequent aggressive interactions between the two species. Crucially however fewer female red squirrels breed and weaned juveniles find it particularly hard to survive in the presence of the greys. Over time as the adult red squirrels age and die, there are fewer and fewer youngsters replacing them and the population progressively declines until it eventually becomes extinct. A similar pattern of decline can be seen in conifer forests. Although in these habitats female breeding may not be particularly affected by the greys, juvenile red squirrels once again find it hard to survive.  In one study the number of youngsters surviving over the winter was found to have dropped from 50% to 17% where there were grey squirrels present.

Did you know?

Local grey squirrel control leads to a dramatic increase in juvenile red squirrel survival and population recovery. See our work in the North of England.

Grey squirrels as a disease threat to red squirrels.

The susceptibility of red squirrels to a disease caused by squirrel pox virus is an additional factor in regional population declines. Infection is characterized by severe skin ulcers and is almost always fatal. Research has revealed that around two thirds of grey squirrels have antibodies to this virus but infection does not cause them any symptoms or adverse effects. Grey squirrels are known to act as reservoir for infection, transmitting it to each other and unfortunately also to red squirrels where the virus causes high mortality rates. This means that even a small number of grey squirrels in an environment present a grave risk to local red squirrel populations.

Did you know?

Scientists are currently developing a vaccine to the squirrel pox virus. This would greatly assist with red squirrel conservation in Northern England and Scotland. RSST also support a successful control project that has limited the spread of infected grey squirrels from spreading north into Scotland.

Interactions between red and grey squirrels.

Both red and grey squirrels are, for rodents, relatively conservative breeders with adult females typically producing one or two litters annually; each of 1-6 young. In contrast there are behavioural differences between the species with greys spending 70% of their time active on the forest floor and red squirrels only 30%. This separation might act to reduce the amount of direct contact between the two species, but as grey squirrels live at much higher population densities in broadleaved woodlands than red squirrels, the high number of individuals’ acts to raise the potential for contact. There is however, relatively little direct interaction between species and when it occurs it appears limited to the occasional aggressive interaction at a point food source. Red and grey squirrels may though use the same tree hollow or drey albeit at different times, and they may also scent mark at the same locations. The possibility of these types of indirect interaction means that there always remains the potential for disease transmission between the species.

Did you know?

Adult red squirrels were once released into Regent’s Park during the 1980s and adults were seen to chase juvenile grey squirrels away from feeding platforms.

Practical conservation.

Research has shown that providing red squirrels with a range of supplemental foods such as sunflower seed can increase populations by up to 50%. However, where grey squirrels are present they too would benefit from this resource, and it is therefore important to make sure that effective grey control is being carried out before starting to feed reds. If control is not in place then there is a risk of squirrel pox virus being spread. Scientists now also suspect that point food sources such as bird tables may also increase the probability of adenovirus spread between red squirrels.

Nest boxes can provide a favourable nest site for red squirrels but should not be erected where there are grey squirrels.

Did you know?

There are a variety of ways that people can get involved in red squirrels conservation and monitoring so if you are interested why not contact Northern Red Squirrels.

Current scientific research projects

There is a range of studies underway that will greatly assist in evolving practical red squirrel conservation.


Aberdeen University Pathogen and viral infections of grey squirrels
AVHLA Wildlife Surveillance Adenovirus and Squirrel pox infection rates in red squirrels
Liverpool University Squirrel pox infection in Merseyside red squirrel populations
London University & Dr Peter Lurz Wildlife stealth cameras as a squirrel population monitoring tool
Galway University Impact of pine marten predation on grey squirrels inIreland
Galway University Landscape barriers to grey squirrel dispersal
Newcastle University Modelling grey squirrel culling and red squirrel population recovery
Edinburgh University Remote sensing as a means of determining woodland habitat suitability for red squirrels
Moredun Institute, Edinburgh Squirrel pox vaccine research
Anglia Ruskin University Coat colour variation in grey and red squirrels



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