Britain's native squirrels are red. The gray squirrels were introduced to Britain from America in the 1870s, and for years they held sway - driving their red cousin into the remotest corners of the country. The upstarts are genetic mutations of grays, but have a darker fur and higher levels of the male sex hormone testosterone - making them more aggressive and more successful. Sex selection is also boosting their numbers because female grays appear to prefer them as mates.The rise of the black is the biggest change in squirrel demographics since the indigenous red squirrels almost disappeared 50 years ago from most of England.
Source: Daily Mail
