Black squirrel
Media playback is unsupported on your device

Scientists track rise of black squirrel

1 February 2012 Last updated at 11:14 GMT

Scientists are urging people to help them track the rise of a relatively new species of squirrel - the black squirrel.

It is thought a number of them escaped from a private collection 100 years ago.

Scientists want to know how far, and how fast, they are spreading throughout Britain.

Keith Doyle reports.