THE Glorious Twelfth, with its tweed-clad shooting parties, is as much a part of the Scottish landscape as fly fishing, stags and ruddy-faced ghillies.

But the future of game bird shooting, a tourism industry worth millions of pounds to the Scottish economy, is under threat from global warming.

A report has revealed that a parasite which preys on game birds is flourishing in our warmer winters. Red grouse stocks are being ravaged by thread worms, which used to die off during the cold months.

The study, by Scottish and American academics, has linked wetter springs and warmer summers to sudden surges in the number of trichostrongylus tenuis worms.

The parasites hatch in the birds’ guts and burrow through their intestines, causing them to starve. The worms also make the birds give off a strong smell, which makes them more vulnerable to predators.

Game birds are under threat from ticks, as well, which are hatching earlier in warmer temperatures and infesting swathes of grouse moor. The blood-sucking parasites can kill up to 80% of bird populations by infecting them with a virus.

Scientists say the parasites threaten the long-term viability of the industry which is already reeling from one of the worst grouse seasons on record.

Scotland has almost 490 grouse moors, which contribute £17m a year to the economy and support more than 700 jobs.

Last year bird numbers on some estates fell by half because of stormy weather during the breeding season. Many estates were forced to curtail shooting to preserve stocks or even cancel all their shoots.

The study, by biologists at the universities of Glasgow and Pennsylvania State, predicts further trouble. By studying bird numbers, temperature and rainfall patterns at 91 grouse moors, researchers found that sudden fluctuations in grouse populations are linked to global warming and growing numbers of threadworms.

Isabella Cattadori, a biologist at Pennsylvania State University, said her study, published in Nature, the scientific journal, raised fears about the “local extinction” of entire populations of red grouse. “We disentangled the mechanism that links climate, parasites and red grouse,” she said.

“Our finding is immensely important to understanding how severe climatic conditions can influence disease emergence, pest outbreaks and extinctions of populations. Theoretical modelling has predicted that global warming will increase parasite transmission and also that transmission will be stretched over longer periods of time.”

Simon Blackett, factor of the Invercauld estate in Braemar, which has several grouse moors, said global warming was already affecting birds. The biggest problem was the huge increase in ticks.

Bert Burnett, an Angus gamekeeper and secretary of the Scottish Gamekeepers Association, said: “With the warmer weather these parasites start to breed earlier. The strongylosis worm is wiping out a lot of grouse in the Borders and the north of England and it does seem to be cyclical. It appears to be at its very worst when grouse numbers are high. Thousands of these little worms are getting into the birds.”

Dr Adam Smith, senior scientist for the Game Conservancy Trust in Scotland, said management strategies were in place that involved dosing with chemicals to kill the worms.

“Lots of things can be done to buffer grouse populations against the possible effects of global warming,” he said.

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