THE oystercatcher is a breed apart - except when it comes to nesting time.

Then anything and anywhere goes, as long as it bears some resemblance to the shingle beaches on which the birds habitually nest.

But one pair have taken things a bit far by setting up home in a car park at the Perth headquarters of Scottish and Southern Energy - leading to a large part of the car park being cordoned off.

Posh and Beaks, as staff at the electricity company have named the wading birds, have already produced a clutch of eggs on the gravel surface. It is the third year in a row the oystercatchers have returned to the same site.

David Sigsworth, SSE generation manager, said: ''We were surprised - amazed - to see the birds return to this site as a nesting ground last year because it is so busy, but they have come back again. We sectioned off part of the grounds for them so we can protect their nest and the young. They take it in turn to chase off predatory seagulls, and even the occasional staff member or visitor who comes too close for comfort.''

The car park oystercatchers are a godsend for any ''green'' profile. Tongue in cheek, SSE can point to the breeding success of Posh and Beaks as another initiative for wildlife.

The energy suppliers already operate bird-friendly accounts in conjunction with the Royal Society for the Protection of Birds, which benefits each time a new account is set up.

But the choice of nesting site by Posh and Beaks will come as no surprise to ornithologists, as oystercatchers appear to lose fear of human proximity at breeding time, leading to a long history of eccentric nesting.

The Scottish Ornithologists' Club has recorded successful oystercatcher breeding on the flat roofs of Monifieth High School, Angus, over 10 years. Two years ago, a janitor found a pair incubating three eggs on a school greenhouse, the door of which had been left open.

Macrihanish Golf Club's badge is an oystercatcher and the sacred rules of golf have been altered to accommodate the waders. A ball landing near a nesting bird merits a free lift and drop.

However, Aberdeen is the roof-nesting capital of Europe for oystercatchers. In the past decade, the birds - the population and range of which have increased across Europe in the past century - appear to have invaded the oil capital as it has expanded on its coastal site.

A study by five ornithologists published last year by the SOC says the Aberdeen city population rose from a few pairs in the early 1970s to at least 275 pairs in the early 1990s, with 205 of these pairs nesting on roofs.

Three factors appeared to be in play - a large number of flat roofs with a surface similar to the birds' original coastal shingle habitat, the proximity in many cases to extensive and frequently-cut grass areas and, third, the oystercatcher habit of carrying food for their young.

Open sites allow the birds to spot predators and the well-maintained grass areas around schools, hospitals, university buildings and industrial sites in the city provide easy feeding.

The colonising habit is catching, with populations establishing on roofs in other towns and villages near Aberdeen such as Stonehaven, Ellon, Whitecairns and Inverurie

Researchers found nest sites as varied as large flower pots, an ornamental pedestal in a driveway entrance, a sports stadium sand pit, the centre of a football pitch and the base of a headstone. Many towns and villages in Holland also have roof nesters, with one district reporting 46 pairs.

The SOC researchers say that leaves Aberdeen out on its own, with probably the highest density of urban roof nesting oystercatchers in Europe. Posh and Beaks are in good company.