IT is commonly believed that they have pushed out their native red-haired cousins thanks to their greater size and strength.
But now researchers have said that grey squirrels may in fact have taken over from Scotland's native red variety in many areas because of their innate cunning.
A study of the two species, which pitched them into a battle of wits, found that greys are much better at solving problems - especially where food is involved.
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The experiment gave wild squirrels two tasks, one easy and one more difficult, with success rewarding them with hazelnuts.
Both species were equally successful at the easy task - opening a transparent lid - but more of the grey squirrels cracked the difficult one, which involved pushing and pulling levers.
Researchers from the universities of Exeter and Edinburgh said this “superior behavioural flexibility may have facilitated their invasion success”.
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Grey squirrels, which arrived from North America in the 19th century, now outnumber red squirrels by more than 15 to one.
Dr Pizza Ka Yee Chow, from the University of Exeter’s Centre for Research in Animal Behaviour, said: "Our research shows problem solving could be another key factor for the success of greys.
“This might be especially important for an invasive species like grey squirrels, as they have evolved elsewhere and have to adapt to their surroundings.”
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