The Grey squirrel is very much a “Marmite species” in Britain, with people tending either to love or hate it. On the one hand Greys represent one of the few species that thrive in our increasingly urbanised country and, as a result, are a species that many people enjoy watching and interacting with in their parks and gardens. Red squirrels are far more arboreal than Greys and this means they’re less easy to observe; they also take less readily to parks and small gardens than Greys. On the other side of the coin, however, Greys are a non-native species, introduced during the 19th century (the earliest verifiable record in 1876, but unconfirmed reports from as early as 1828) and arguably now represent one of the most invasive species in the UK.
Today, Greys have expanded their range throughout most of mainland Britain and parts of Ireland and have continued to increase their range even in the face of sustained persecution from humans. Projects are still underway that aim to remove the species from key Red squirrel habitat in the UK, but it remains to be seen how successful this will be in the long term. In the meantime, many people enjoy the antics of probably the only squirrel species they’d be likely to see in their small city gardens.
The Grey squirrel at a glance
Size: Max. 55cm (~2ft), of which 25cm (10 in.) may be tail; average about 26cm (~1ft) including tail. Weigh from 400 to 700 grams (14–25 oz.), with most specimens across Europe between 450 and 650g (16 – 23 oz.); average about 550g (19.5 oz. – seasonally variable) in UK.
Colour: Typically grey-backed, grey tails and white (or significantly lighter) underside; flanks vary from grey to dusky red. Melanistic and albino Greys rare; white individuals may be locally common.
Distribution: Native to oak-hickory forests of eastern NE America; first recorded introduction was to Cheshire in 1873, but may have been present since late 1820s. In UK, Greys found throughout England, although they’re absent from Isle of Wight and apparently scarce from north Pennines to Southern Uplands (ca. 56o to 54o N). Fragmented populations exist in Scotland, Wales and Ireland.
Longevity: Oldest captive specimen was 20 yrs; Wild ave. 4-5 yrs for females and 2-3 yrs for males.
Sexing: Impossible at distance; during breeding season close inspection reveals swollen testes. Distance between genital openings can be used to sex squirrels during handling.
Activity: Diurnal; seasonally sporadic activity patterns. Active throughout day during autumn; activity diminishes to about 4 hours or less (mornings) in winter, before increasing again to between 3 and 8 hours — frequently bimodal — in spring and summer.
Dens: Referred to as “dreys”, usually in trees (occasionally on ground). Composed of leaves and twigs; lined with moss. Roughly spherical and typically 30cm (1ft.) diameter. Nursing females may have several dreys in area to facilitate moving young when threatened.
Territory: Range over between 2 and 10 hectares (5 to 25 ac.) for most of year, but males may cover more than 100 ha (247 ac.) during mating season. Defend core area from intruders; parts of range may overlap.
Diet: Primarily seeds and plant matter, incl. berries and fruit. Opportunists; diet includes fungi, nuts, seeds, bark, sap, soil (minerals?), roots, cereals, insects (incidental?), bird chicks and eggs and human rubbish.
Reproduction: Produce 1 or 2 (if mating begins in December) litters of 2 to 4 kittens (ave. 3, max. 8), following 42 to 45 day gestation. Peak of mating/chasing during January. Litters produced during spring (mid February-late April) if good crop of mast, or summer/autumn (mid July-mid November) if crop less bountiful – occasionally, litter in both seasons. Kittens eat solid food and leave drey at about 7 wks; weaned by 10 wks. Sexually mature at 10 months to 1 yr old.
Behaviour & Sociality: Primarily solitary; drey sharing known, individuals seem familiar with each other. Hierarchy system known between and within sexes; males not necessarily dominant to females. Peak dispersal in autumn (some in summer and spring). Spend more time on ground than Reds. Emit several acoustically distinct calls; foot stomping, tail flicking and chasing my accompany agonistic calls. During breeding season, single female may be pursued by several males. Chasing, chattering and tail-flicking often witnessed during mating chases.
Threats: Widely persecuted in the UK as part of Red squirrel conservation plans – implicated in Red squirrel and native bird decline. Many killed on roads. Persecuted as a pest to forestry. Globally, predators include foxes, wildcats, martens, goshawks, raptors, stoats, coyotes, snakes and bobcats.
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