red squirrel in Dumfrie-shire, taken by Crafty Green Boyfriend. This squirrel isn't typical as it has lost half of one of its ears
Red squirrels the slim, cute squirrels beloved of Beatrix Potter's Squirrel Nutkin andother stories have long been out-competed by the heavier grey squirrels that were originally introduced from the USA. The grey squirrels threaten the reds through outcompeting them and also be passing on a squirrel pox disease that affects the reds badly but that the greys are immune to.
In many parts of Scotland, the red squirrels still hold their own, but in Edinburgh we only have grey squirrels. In the absence of reds, the greys are appealing animals to have in parks and gardens, though they can be a menace eating all the seed from birdfeeders.
However in areas where there are both red and grey squirrels conservation measures are in place (or being put in place) to conserve the native reds and keep out the greys. These may include establishing buffer areas around the red squirrel strongholds with control of grey squirrels, ongoing monitoring, helping landowners to improve habitat for squirrels, involving local schools and communities and using forest planning to maximise the value of forests for squirrels. Also the recovery of the pine martin (a woodland predator related to stoats) can help red squirrels to recover in number as the larger grey squirrel can't run away from the pine martin quickly enough and is more likely to be eaten than the speedier reds!
There's a really interesting article (with some very cute photos!) about red squirrels on the BBC website here.
The Wildlife Trusts hold Red Squirrel Week every year to raise awareness of the lovely red squirrel. You can find out more here.