RESIDENTS in the small Ayrshire town of Muirkirk will learn today it is about to become the centre of one of the largest protected nature reserves in Britain - thanks to local farmers.

Naturalists will inform a public meeting that 27,500 acres of the surrounding hills and moorlands are about to achieve site of special scientific interest (SSSI) status in a bid to protect the countries largest breeding population of hen harriers.

Bordered by the A/M74 in the east, the site will stretch about 15 miles from the A71 Irvine Valley road south to the North Lowther Hills close to Sanquhar. The Cairngorms is the only larger designated SSSI in the country.

Mr Graeme Walker, of Scottish Natural Heritage in Ayr, reports that the area supports 28 breeding pairs of the bird, but with a country wide population of just 480 pairs, that is 6% of the British population The species has red for in danger status in the RSPB Birds of High Conservation Concern listing and has been in major decline throughout Europe. It is listed too in Annex 1 of the 1979 European Commission Birds Directive.

But lucky hillwalkers in East Ayrshire can see this rare predator in action - the grey-backed male, its black tipped wings spanning a metre or more, or the brown female - quartering their hunting area at a low, slow glide in search of prey.

And, says Mr Walker, the East Ayrshire comeback is due entirely to the farming community. ''Hill farmers are managing the moors for sheep,'' he says. ''This gives a mix of short and long heather and grass which is ideal.''

Hen harriers, he points out, feed on voles, mice and small birds found in the grassland but nest in long heather. ''The land management produces the optimum mix of prey to feed on and areas in which to nest. This is a man-made habitat.''