A new study suggests that the grey squirrel has beaten the red squirrel to the finish line in terms of size, population, and even problem-solving skills. The former, who arrived in the UK from North America in the 19th Century, has been deemed more adaptable than the native red squirrels of Britain.

Researchers conducted a series of tests where the squirrels had to retrieve hazelnuts by making their way past a certain obstacle.

The first task involved retrieving a hazelnut from a sealed container. Results showed that both species were equally capable when it came to opening a transparent lid.

The second task, however, added more complexity -- it required the pushing and pulling of levers to retrieve the hazelnut. Ninety-one percent of the grey squirrels were able to solve the harder task as opposed to 62% of the red squirrels.

Researchers explained that red squirrels may not be as efficient as their grey counterparts in gathering food. This could have led to declining fitness over the years in addition to low levels of breeding.

Of the squirrels used in the study, the grey ones were from Exeter and the red ones were from the Isle of Arran, off the west coast of Scotland.

Dr Pizza Ka Yee Chow, from the University of Exeter which led the study, told the Daily Mail, "Many factors have been considered to explain why grey squirrels are more successful when they move into areas where red squirrels live. These factors include disease resistance and the fact grey squirrels are bigger, but 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."

Today, greys have outnumbered reds by more than 15 to 1. There are more than three million greys in the UK, while just 30,000 of reds remain in England, 120,000 in Scotland and around 1,500 in Wales.

The red squirrels did see victory in parts of their attempts. Some of them were said to react more quickly than the grey squirrels during the difficult task. They were also quicker to try out a new strategy when a tactic did not work.

Professor Stephen Lea, also from Exeter's Centre for Research in Animal Behaviour, hoped that the research would give them a better insight into the future and survival of both the species.

The study, which is titled "A battle of wits? Problem-solving abilities in invasive Eastern grey squirrels and native Eurasian red squirrels" was published in the journal Animal Behaviour.