At almost twice the size of the native Red Squirrel Sciurus vulgaris, the Grey Squirrel Sciurus carolinensis has a mean head and body length of 260 mm and weight ranging from 440-650 g (male) and 400-720 g (female). The coat appears grizzled silver-grey, although the individual hairs are banded brown, black and white, with some orangey-brown along the mid-dorsal region and flanks, especially in summer. The tail is silver-grey with a white ‘halo’. The underside is white. There are no conspicuous ear tufts (Harris and Yalden, 2008).
A melanistic morph, uniformly jet black, was first reported in Letchworth in 1912 (Middleton, 1931) and is now becoming fairly common in the south of England. Black squirrels interbreed readily with the wild-type colour and they live in mixed populations of grey and black. Dark/black Grey Squirrels are also present in Sunderland (Kevin O’Hara, pers. comm., 2012). Less commonly, albino morphs can occur as can an intermediate colour, which is brown-black with an orange/tan underside (Shorten, 1962a; McRobie, 2012). Examples of Grey Squirrels with varying degrees of orange/tan on the underside have been found near Prudhoe, Northumberland, in spring 2012 (Northern Red Squirrels Newsletter, Spring 2012).
Grey Squirrels are diurnal, do not hibernate and swim well should the need arise. They can breed all year round with mild weather and a good food supply, produce up to seven kittens per litter (average three) and can live for up to nine years in the wild (20 years in captivity). Population density can be up to more than eight per hectare in oak woodland but much lower in conifer habitats, varying with the proximity of broad-leaf woodland. They spend only an average of 14% of their foraging time in trees. The total British population estimate is 2.52 million (Harris and Yalden, 2008).
Squirrels can generally be identified by their feeding signs (Stehli and Brohmer, 1965) but it is difficult to reliably distinguish between Grey and Red Squirrels in this way and direct sightings are recommended to confirm presence to species level (Gurnell et al, 2012).
Grey Squirrels are native to the dense hardwood forests of the eastern states of North America, from Ontario and New Brunswick in Canada to Florida, USA. Anthony (1928) distinguishes two sub-species in the squirrel’s native range. S. carolinensis carolinensis, the Southern Gray Squirrel, is the smaller of the two and inhabits the southern part of the species’ overall range as far north as the lower Hudson Valley. S. carolinensis leucotis is “larger and grayer, and apt to occur in black or melanistic phase, with various degrees of intergradations occurring”. Its distribution is more northern, including Pennsylvania and southern Ontario (Laidler, 1980). Shorten (1962a) states that there are actually five sub-species of Grey Squirrel in North America, but these two sub-species are probably the only ancestors of the Grey Squirrel in Britain.
During the 19th century “gray” squirrels attracted the attention of gentlemen travelling in America, who decided that they would be an “aesthetic addition to the fauna of the British countryside” (Laidler, 1980). Laidler (1980) cites records of Grey Squirrels in Britain as early as 1828, but says these seem to have disappeared. All authors agree that the first recorded successful introduction was in 1876, when Mr T. V. Brocklehurst released four Grey Squirrels from the USA into Henbury Park, near Macclesfield, Cheshire.
In 1889, Mr G. S. Page released five Grey Squirrels into Bushey Park, Middlesex, but this introduction was apparently unsuccessful, so he tried again, importing 10 squirrels from the USA in 1890 which were released at Woburn Abbey, Bedfordshire, by the 9th Duke of Bedford. The offspring of these squirrels were subsequently introduced into eight areas of England, one of which was in Malton, Yorkshire in 1906, where 36 animals were released. There were two more introductions into Yorkshire (Bedale in 1913 and Bingley in 1914) and one into Darlington in 1914-15, though the sources of these animals is unknown (McRobie, 2012; Laidler, 1980). Grey Squirrels continued to be imported and translocated into new sites across Britain until at least 1929, and probably up to 1937, with 32 recorded introductions altogether (McRobie, 2012). Laidler (1980) suggests that it almost became a ‘fad’. In common with other wild fauna, they were also kept as pets.
Populations grew rapidly. Three animals of the Canadian sub-species were released at Loch Long, Argyll and Bute in 1892 (McRobie, 2012) and by 1915 the resulting population had “expanded their range to 300 square miles, an average increase of twelve square miles each year” (Laidler 1980). Watt (1915), cited in Barrett-Hamilton and Hinton (1910-1921), describes the introduction into Woburn as “an embarrassing success, because they increased so rapidly that it became desirable to reduce their numbers, and it was stated that about 1000 were killed during a recent winter, and 300 in one week”. Watt also comments on their destructive nature: “As regards habits, the grey squirrel, like the native brown squirrel, has many offences laid to its charge … It is very destructive to the upper shoots of Scot’s Pines, … causes much trouble in the kitchen garden, among the aviaries and poultry runs, and in the woods of deciduous trees, and they also raid the gardens for small fruit, … and dig up crocus bulbs. … They are inveterate destroyers of eggs and young birds. In the Zoological Gardens they have been observed taking birds eggs, or, if the young are hatched, they pull them out or destroy the nests.” Meanwhile, the squirrels released in Malton “multiplied and spread so rapidly, and were found to be so destructive that most of them have been got rid of after three years constant warfare” (St Quintin 1914, in Barrett-Hamilton and Hinton, 1910-1921).
Naturalists soon began to notice that as Grey Squirrels became established in an area Red Squirrels usually began to disappear. For example, at Kew (another Woburn-sourced release site) “it was stated that they have killed out or driven away all the native squirrels” (Barrett-Hamilton and Hinton, 1910-1921). Mee (1922) reports: “they have driven out our red squirrels from Richmond Park, they have banished them from woods and gardens.” Douglas Middleton published the first research papers on Grey Squirrel ecology in 1930 and 1931 and dismissed these early popular beliefs, showing that although aggressive encounters did occur, they were not common, and just as likely to be intra-specific as inter-specific.
The government eventually decided to attempt to control the spread. The Grey Squirrel Prohibition of Importation and Keeping Order was passed in 1937, which made it illegal to bring a Grey Squirrel into Britain, or to catch and keep the species as a pet. Subsequently, between 1953 and 1958 a bounty system was introduced. Gun and shooting clubs received subsidised cartridges, with a bounty of one shilling (5p), later increased to two shillings per tail. Squirrel recipes were distributed (Bob Wilkin, pers. comm., 2012). Overall the system was unsuccessful, with the number of squirrels present being estimated as roughly the same in 1958 as it had been in 1953. The conclusion drawn from this was that while they could be removed this way from a local area, other squirrels would quickly recolonise from surrounding areas (Shorten, 1962b; MAFF, 1960-62).
Locally, naturalists comment on the spread of the Grey Squirrel and decline of the Red in northeast England over the course of the last century: “From around 1950 it was usual to see squirrels in the South Park, Darlington, and they were all Grey” (Griss pers. comm., 2012). Several surveys have been conducted and reports published. A single Grey Squirrel was recorded in Alnwick in 1930 (Lever, 1977) and another in Gosforth in 1945 (Strong, 1945), but neither of these animals seems to have reappeared. In 1953 Temperley conducted the first squirrel survey across Northumberland and County Durham. He mentions the Darlington introduction and states that Grey Squirrels began to colonise Raby Park, Staindrop, just before or during World War II, where “attempts were made to exterminate them, but … without success”. They were seen occasionally in other areas: north of the Tees around Stockton, and south around Middlesborough. Apart from these, all surveyors, from both County Durham and Northumberland, reported an absence of Grey Squirrels in their area.
In 1965 Ashby stated that the Tees still “formed the approximate boundary between the zone occupied by the grey squirrel to the south and the red squirrel to the north. … In the dale itself, most of those seen below Middleton in recent years have been grey squirrels and most of those above have been red”. But by 1972 Tegner was reporting that “Grey squirrels have seemingly crossed the Tees into south Durham as they have been recorded in the county.” He implies that they were still rare, and up until 1977, according to Lever, “the principal areas of grey squirrel distribution were still considered to be south of the River Tees”.
Davis (1979) conducted another survey in 1977/1978 across “Northumberland, Tyne & Wear, Durham and Cleveland”. His results highlighted the continued spread of Grey Squirrels, finding that they had been present in every hectad in the southernmost areas of County Durham and Cleveland since at least 1959 (see also Arnold (1993) who agrees with this statement). From there they had spread north, particularly into western County Durham by 1971, and had spread further north by 1977/78; however he found no evidence of Grey Squirrels in Northumberland.
The first Grey Squirrel sighting to be recorded on the regional database was “one count of deceased” at Gilsland Bridge on the Cumbrian Border in 1905. There was then a long interval until the next record, which was just west of Crook, County Durham in 1968. By the 1970s, the database records that Grey Squirrels were sparsely distributed across County Durham; recorded in Teesside by 1975 and at Washington/Fulwell and High Force, Middleton-in-Teesdale in 1977.
During the 1980s single Grey Squirrels were seen in Throckley Dene and Gosforth, Newcastle. However, these are thought to be releases/escapes. The first Grey Squirrel sighting in Northumberland to be recorded on the regional database was in Hexham in 1989. From the early 1990s onwards Grey Squirrel distribution continued to expand. Our map shows that they have now been seen in almost all of the hectads in our region.
Grey Squirrels are regarded as pests in Britain. DEFRA (2012) states that “The grey squirrel is an invasive alien species which damages woodlands and may have negative impacts on biodiversity in addition to its confirmed impact on red squirrels. It is listed under Schedule 9, Part 1, of the Wildlife & Countryside Act 1981. This means that any person who releases a grey squirrel, or allows it to escape into the wild, is guilty of an offence.”
Written by Veronica Carnell (last updated Nov 12)