Winter sports such as snowboarding, off-piste skiing and trekking are putting Alpine wildlife under stress, scientists have concluded.
Researchers found that in areas of the Alps heavily used for sports, black grouse produced large amounts of a hormone indicating stress.
Writing in the Royal Society's journal Proceedings B, they say these sports represent a new threat to wildlife.
Climatic change is also affecting habitat for these birds.
During the winter, they make burrows, or "igloos", in the snow. They come out twice each day to feed, then make a new igloo in which to hide.
Rising winter temperatures are reducing the availability of these hiding places on lower slopes, while this new study, by scientists based in Switzerland and Austria, suggests the growing popularity of "extreme" winter sports is affecting their chances higher up the slopes.
In a wide variety of animals, production of the hormone corticosterone rises in conditions of stress.
Black grouse are apparently no different.
In the first part of their study, the research team tagged three of the birds for identification. They then put them under stress for several days by repeatedly forcing them out of their snow burrows, mimicking conditions the birds face in areas heavily used for human recreation.
Signs of stress were evident in the birds' faeces in the form of elevated levels of corticosterone.
"Extreme" sports are taking people into more remote parts of the Alps
The second part of the study involved collecting black grouse faeces left in 32 sites, some close to winter sports centres and others in unused parts of the mountains.
Birds closer to human sites produced higher levels of corticosterone, the stress marker.
Stress can affect animals in a variety of ways, potentially affecting even reproduction, though this study did not look for or find any specific impacts of the elevated stress.
But there may be other factors too. Increased disturbance may mean birds leaving their igloos more frequently, exposing them to cold and predation.
More research would be needed to measure these impacts and to extend the analysis to other species. Looking at other regions used for winter sports would be another approach.
But the research team, led by Raphael Arlettaz from the University of Bern, believes Alpine wildlife might need extra protection as winter sports and winter melting spread.
"Only the creation of suitable protected wintering refuges will enable the Alpine fauna to endure the growing pressure exerted by human activities on these vulnerable mountain ecosystems," the scientists write.