Miracle on the grouse moors

Yet the elation was almost palpable among participants at a grouse seminar held at Ripley Castle last week.

Just five years ago, red grouse numbers were said to be on a downward and seemingly irreversible slide, with virtual annihilation of the species in the UK seen as a real possibility.

Beset with a parasite called Trichostrongylus tenuis – a threadworm which lives in the guts of red grouse and burrows through its intestines causing them to starve – the grouse's distinctive whirring of wings and "goback-goback-goback" alert call when flushed from heather had become almost a nostalgic memory in some areas.

Instead, those birds afflicted with the condition, known as strongylosis, glided weakly away. Some of them were even too weak to take to the air and sat down, fair game for predators such as the fox.

But now the tide seems to be turning, and the grouse moor owners, estate managers, agents and gamekeepers meeting at Ripley heard how the species – and the sport of grouse shooting – have been rescued.

The key factor is the development of a new treatment for strongylosis, Dave Newborn, the Swaledale-based senior grouse scientist with the Game & Wildlife Conservation Trust, told the seminar.

Strongylosis isn't new – it's been around for a century – and since the 1970s the worms in red grouse caused fluctuations in their numbers, producing population crashes. By the early 1980s, the search for a cure focused on finding a reliable method of getting medication into the grouse. Within a few years, Newborn was conducting trials with medicated grit.

Grouse consume a great deal of quartz grit, which occurs naturally on moorland. It helps their digestive systems to grind up the tough heather which makes up 80 per cent of their diet. Boxes containing grit treated with an athelmintic drug – the same worming medication as used for domestic pets - were placed on moors, but for years it was only partially effective. Now, large scale trials with more effective grit on about 30 moors in northern England have produced some spectacular results. Some blocks of moorland were provided with medicated grit and here July counts showed just under 300 birds per square kilometre compared with under 200 birds on non-medicated plots with up to 98 per cent fewer worms. Newborn's follow-up studies revealed that 16 per cent of adult red grouse tested now had no worms. "We'd never seen that before," he told the seminar. "I even went to the opticians half way through the count to make sure I wasn't missing them. I got very excited."

Those birds which were caught and tested for worms revealed that their "worm burdens" were much lower than before. Up to 40 per cent had fewer than 100 worms, against a previous norm in excess of 3,000. Before declaring that the problems of grouse moors had been "cracked", however, Newborn flagged up some potential adverse consequences.

One was that the medication success might lead to too many grouse. Would there be enough sportsmen to deal with the increased numbers? And would larger grouse stocks produce new problems? For example, another parasite might step in to fill the gap.

Or the Trichostrongylus tenuis could possibly build up resistance to the medication, as often happens with a treatment.