Today (Friday) is Red Squirrel Appreciation Day in the UK, but what many people do not know is the grey squirrel, seen on country walks and in their gardens, is an invasive species and the arch enemy of our reds, chiefly responsible for their dramatic population decline across Britain.

Red squirrels (Sciurus vulgaris) are native to the UK, greys (Sciurus carolinensis) are from North America and were imported as a novelty species into UK parks and gardens from the 1870s. They are not reproductively compatible. As a consequence, the red population in Britain has plummeted from millions to approximately 287,000 The greys have largely replaced them.

"This dramatic decline is caused by a number of factors. Greys are larger and stronger and out compete red squirrels for food and habitat. Another serious problem is that some of them carry the deadly squirrel pox virus that does not harm them but is fatal to reds.We believe the majority of people in England have never had the joy of watching our native red squirrel in the wild and know only the grey. This is something we want to change," says Vanessa Fawcett of the Red Squirrel Survival Trust.

If you have been lucky enought to capture a Pembrokeshire red squirrel on camera, why not send your photo to the Observer by emailing [email protected] or share it in the ’Picture This’ Facebook group?