Ski resorts have a profound impact on wildlife, according to a study of a declining bird species in the Alps.
In the first investigation of the direct effects of skiing on wild species, the researchers have shown that stress levels in the black grouse are raised by disturbance from skiers and snowboarders. They believe this is part of the reason for the bird's scarcity around ski resorts and may be a factor affecting other species such as snow hare and red deer.
The finding adds to the list of eco-crimes that have been laid at the door of ski resorts. Bashing pistes to smooth the surface for skiers and using artificial snow have both been shown to change the vegetation on ski runs and tree felling to make way for pistes has a profound effect.
Environmentalists also condemn the carbon dioxide emissions associated with flying holidaymakers to the resorts.
The black grouse, which occurs throughout the Alps and in Wales, Scotland and the Lake District, typically exists at half its normal population density around ski resorts and the effect of human disturbance appears to be increasing as more skiers go off piste.
"More and more people want to enjoy nature," said Raphael Arlettaz at the University of Bern's zoological institute in Switzerland. "The impacts are becoming more and more intense outside of the ski resorts."
He and his colleagues looked to see what effect disturbance was having on the birds by examining the levels of a stress hormone in their droppings. They divided 32 sites across south-west Switzerland into low, moderate and high disturbance regions and found that even moderate disturbance was enough to raise the levels of the stress hormone corticosterone.
To really pin down human disturbance as the cause they artificially raised stress levels in some birds by deliberately flushing them out of the snow "igloos" they occupy between bouts of feeding. This raised the birds' stress hormone levels the next day, the team report in the Proceedings of the Royal Society B.
Dr Arlettaz believes higher stress levels contribute to the birds' decline in disturbed areas because of the energy costs they suffer being forced into the cold air.
He said that other species that occupy prime ski resort areas are red deer, ibex, chamois, roe deer, rock partridge, snow hare and ptarmigan. All may be affected in a similar way by disturbance, although no one has studied stress effects in these species directly.
To mitigate the problem, he said resorts needed to designate no-go areas where there is no interference even by off-piste skiers. "These places can be quite small. They don't need to be whole slopes," he said.
Such a solution will not solve other problems though. A 2005 study in 12 Swiss ski resorts found that just maintaining the pistes has significant ecological effects.
The researchers compared 38 plots on pistes with 38 similar plots nearby. They found that ski pistes had lower plant species richness and productivity. There was also lower abundance and cover of woody plants and early flowering species.
This makes sense because the compacted snow on ski pistes shortens the growing season by covering the ground later into the spring. The use of artificial snow also caused changes to the collection of plants found on the piste.
Aware of the marketing opportunities of trumpeting their green credentials - and the pitfalls of losing eco-conscious skiers - some resorts have begun to change the way they operate.
The Three Valleys of Couchevel, Meribel and Belleville now use entirely hydroelectric power for their electricity requirements - including 1,920 snow cannons and 183 ski lifts. They also use biodegradable diesel for all company vehicles and all old lift installations are dismantled and recycled after their working life.