Grey squirrel

Latin name
Sciurus carolinensis

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 Eastern Grey squirrel (Sciurus carolinensis). - Credit: Marc Baldwin

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, although most probably survive less than 2 yrs.

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. Various calls including aggressive 'quaa-ing' and 'chittering' (made by rubbing incisors) when disturbed, often accompanies by flicking of tail. Droppings are dry, tubular ~1cm (0.4 in.) long and deposited during activity (i.e. not in latrines).

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 to late April) if good mast crop, or summer/autumn (mid-July to mid-November) if crop less bountiful – occasionally, litter in both seasons (i.e. mating in January and June). May skip breeding altogether if mast is poor during previous autumn. 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 and chasing appears important part of successful copulation. Chasing, chattering and tail-flicking often witnessed during mating chases. Kittens engage in solitary object-play and social play, including chasing and pseudo-copulation (sometimes male-male); solitary play persists in adults and includes erratic rolling, jumping and darting around.

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.

Grey squirrel in detail


Atlas of the Mammals of Great Britain & Northern Ireland - by Multiple Contributors
Pelagic Publishing -- 2020 -- ISBN: 978-1784272043

Britain’s Mammals 2018: The Mammal Society’s Guide to their Population & Conservation Status - by Multiple Contributors
The Mammal Society -- 2020 -- ISBN: 978-0993567339

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Vulpine Publishing -- 1987 -- ISBN: N/A

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HarperCollins Publishers -- 1993 -- ISBN: 978-0002197793

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Mammals of the British Isles: Handbook, 4th Edition - by Stephen Harris and Derek Yalden (eds)
The Mammal Society -- 2008 -- ISBN: 978-0906282656
The natural history "bible" covering all British mammals with detailed coverage of their biology, behaviour, ecology and taxonomy written by experts in the field and referenced to the primary literature.

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New Holland Publishers -- 2003 -- ISBN: 978-1845171131

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Oxford Univesrity Press -- 2007 -- ISBN: 978-0199548156

Simon King’s Wildguide - by Simon King
BBC Books -- 1994 -- ISBN: 978-0563364962

Squirrel on my Shoulder - by John Paling
BBC Books -- 1979 -- ISBN: 978-0563176398

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Collins -- 1954 -- ISBN: 978-1616905774

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Whittet Books -- 1987 -- ISBN: 978-1873580172

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Kingdom Books -- 1998 -- ISBN: 978-1852790288

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Isabelline Films -- 2015 -- ISBN: N/A

The Encyclopaedia of Mammals - by David MacDonald (ed.)
Brown Reference Group -- 2006 -- ISBN: 978-0199206087

The Grey Squirrel: Ecology & Management of an Invasive Species in Europe - by Craig Shuttleworth, Peter Lurz & John Gurnell (eds.)
European Squirrel Initiative -- 2016 -- ISBN: 978-0954757649

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Christopher Helm Publishers -- 1987 -- ISBN: 978-0747012108

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New Holland Publishers Ltd. -- 2009 -- ISBN: 978-1847734549

The New Amateur Naturalist - by Nick Baker
HarperCollins Publishers -- 2004 -- ISBN: 978-0007157310

The Red Squirrel: Redressing the Wrong - by Charles Dutton
European Squirrel Initiative -- 2004 -- ISBN: N/A

The Wildlife Trust’s Handbook of Garden Wildlife - by Nicholas Hammond
Bloombury -- 2014 -- ISBN: 978-1472915863

UK Mammals: Species Status & Population Trends - by The Tracking Mammals Partnership
JNCC/TMP -- 2005 -- ISBN: 978-1861075680

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Whittet Books -- 2012 -- ISBN: 978-1873580851

Urban Wildlife - by Peter Shirley
Whittet Books -- 1996 -- ISBN: 978-1873580233

Wild Animals of Britain & Europe - by Helga Hofmann
HarperCollins Publishers -- 1995 -- ISBN: 978-0007627271