Despite being two different species of squirrel the grey and red squirrel do share some similarities, says Mark Henderson from the Red Squirrel Survival Trust.
Both squirrels are arboreal (tree dwelling) and diurnal (out and about in the day). Their primary food source is generally the nuts and seeds of trees, but is supplemented by fungi, fruits, leaves, buds, nectar and sometimes songbird eggs and nestlings.
Their tails are roughly equal in length to their entire body.
There are two mating seasons during the year, assuming they are well fed and healthy and produce a similar litter size of 3 to 6 kits. Their nests are called dreys and are an untidy “football-sized” ball of twigs but are difficult to spot from the ground. Unlike birds’ nests, they are built very close to the trunk or in strong forks and most squirrels will have two or three dreys and move between them.
However, there are considerable differences…
What’s the difference between a red squirrel and a grey squirrel?
Red squirrel vs grey squirrel: appearance
Grey squirrels are larger and heavier than red squirrels. Greys average 48cm (including tail) in length which is 26 per cent/10cm more than the average for reds. In weight however, the greys average 575g compared to the red average of 305g, a difference of almost 90 per cent in favour of the more stocky/muscular grey.
Telling the difference based on colour only can be difficult as greys can have a red/brown tinge to their fur, and reds, particularly those that originate from Northern Europe/Scandinavia can grow a noticeable grey winter coat.
Almost all reds will grow the characteristic ear tufts but only during winter. The safest way to tell them apart is to look at the tail. The grey squirrel tail fur is white coloured at the end. This gives a sort of halo/shimmer look, whereas the red squirrel tail fur is all the same colour.
Red squirrel vs grey squirrel: diet
The grey, whilst eating the same as the red, has a competitive advantage in that it can eat seeds and nuts before they have fully ripened. Its digestive system can cope with the tannins whereas the red squirrel’s cannot. This means that the greys can access and deplete the food source earlier.
Of great concern is the tendency of both squirrels to strip bark from particular juvenile trees (oak, beech, hornbeam, wild cherry etc.) to get at the sap.
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Red squirrel vs grey squirrel: habitat and population densities
It is a myth that red squirrels prefer pine forests and greys prefer mixed broadleaf woodland. Both prefer mixed broadleaf and the nut and seed supply from that type of woodland/forest. Reds have been forced out into pine forests as the greys dominate the food supply. One hectare of perfect woodland can support one red squirrel whereas it can support anything from three to thirty grey squirrels.
Native and non-native invasive species
The red squirrel is native to the UK and has existed frm the ice age. The grey was imported to the UK and Ireland from the late 1870s to the early 1900s.
Greys were released accidentally and deliberately and have spread to all but islands (Isle of Wight and Brownsea) and the highlands of Scotland. Estimates for numbers vary but for reds, it is 120k–160k across the UK with fewer than 15k in England and approximately 100k in Scotland. Across Cambridgeshire, Hertfordshire and Bedfordshire, there are some 20k black squirrels. These are in fact a melanistic version of the grey and were also imported from the USA. Research suggests that this squirrel originated from a cross between the American grey and the fox squirrel in the USA.
Red squirrel vs grey squirrel: threats
The main threats to all squirrels are cars, predation from domestic pets and habitat loss. For red squirrels the added threats come from grey squirrels. They simply cannot compete for food with the larger, heavier, hungrier competition and through this alone, would normally either retreat to less favourable woodland forest or simply die out within a few generations. Sadly, the grey also has “an accelerator” in the form of the parapox virus. Greys carry this virus with no threat to themselves but if transmitted into a red population, it can decimate the red squirrel numbers within weeks. For these reasons, co-existing is simply not possible and as they are different species, they will not cross breed.