Seventy-five per cent of the UK's red squirrels are found in Scotland. This species faces threats that include competition from the introduced grey squirrel, and the 'Scottish Strategy for Red Squirrel Conservation' provides a framework for supporting its long-term conservation. Research in 2007 credited the growing population of pine martens with assisting this programme by preying selectively on the grey squirrels. Scotland has no population of the edible or hazel dormouse, or of the yellow-necked mouse, and the harvest mouse's range is limited to the southern part of the country. The St Kilda mouse and Orkney vole (see above) are endemic, but otherwise population distributions are similar to the rest of mainland Britain. Colonies of black rats remain only on the island of Inchcolm in the Firth of Forth and on the Shiant Isles.