07/03/2007
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Free-riding Snow Sports, a Novel Serious Threat to Wildlife

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Black Grouse (photo: John Anderson).

A recent study by the Universities of Bern and Vienna and by the Swiss Ornithological Institute show that the most trendy snow sports, like free-ride skiing and snowboarding or snowshoeing, which are developing massively in the Alps, are also threatening the survival of Alpine wildlife, pushing them to their last hide-outs.

Alpine wildlife has developed unique adaptations to confront the severity of winter climate. During the cold season, the energetic balance of mountain animals must be so finely tuned that minimizing energy expenditures is an absolute priority, especially as food is scarce in winter. Any external disturbance could alter these subtle physiological adjustments, leading to critical energy loss. Beyond a certain point energy loss can no longer be compensated for, compromising health and winter survival.

The massive development of winter sports in the last decades has made the Alps a prime winter tourist destination across Europe. This has come along with radical changes in Alpine ecosystems. Vast areas of remote habitats which remained untouched during the whole winter in the past are now visited daily by thousands of tourists between December and March. The native fauna can not always adapt to these unprecedented human intrusions.

Swiss and Austrian scientists have analysed the physiological response of an emblematic, declining Alpine species, the Black Grouse, which dwells in the skiers' favourite landscape: the semi-open, shrubby habitats at the interface between dense subalpine forests and high-altitude pastures. The researchers had to develop a non-invasive method that allowed them to measure the stress levels of the birds without needing to capture them. Capture would constitute a source of disturbance, affecting not only the birds but also the results of the research! The technique chosen involved analysing the concentrations of metabolites of corticosterone (the stress hormone of the birds) in faeces. During winter Black Grouse spend most of their time (more than 20 hours a day!) within snow-burrows, which they dig twice a day: one igloo in the morning after breakfast, and another one at dusk after a frugal dinner. This way, they are thermally insulated from the outside and can reduce energetic losses to a minimum, while at the same time they are protected against predators. The faeces of the birds accumulate in the bottom of their igloos. When Black Grouse over-wintering grounds are known, it is easy to locate old igloos and recover the faeces, which can later be analysed to measure their stress-hormone metabolites content.

Black Grouse (photo: John Anderson).

A research team led by Prof. Raphaël Arlettaz (University of Bern and Swiss Ornithological Institute) has, in the first place, evaluated chronic stress levels (long-term accumulation of stress effects) to which the birds are exposed, compared with man-made pressures, in:

  • natural environments (with no, or extremely low, human pressure)
  • areas with moderate human pressure (dedicated to mountaineering skiing, free-riding skiing or snowboarding, and/or snowshoeing)
  • areas close to ski resorts with intense human pressure by snow sports

The results clearly indicate higher-than-average levels of the stress-hormone metabolites in both categories of habitats with moderate and intense human pressure, relative to areas with almost no human pressure. On the contrary, areas with moderate and intense pressure did not differ from one another. This shows that even a moderate disturbance, such as the one provoked by groups of skiers, snowboarders, snow-shoers, free-riders, etc., are troubling to the birds.

The researchers also conducted disturbance experiments with wild-caught, free-ranging Black Grouse equipped with radio-transmitters, a technique which enables the identification and location of individual birds. The birds were experimentally flushed from their igloos during several consecutive days so as to mimic a situation of acute stress typically generated by sudden, and repeated, human disturbance. The results were again unequivocal: a 60% rise in the concentration of stress-hormone metabolites took place between the period with no disturbance (control) and the subsequent days when flushings were deliberately performed.

These results provide for the first time a quantitative measure of the physiological effects of snow sports on Alpine wildlife. The scientists are now investigating the impact of these human winter disturbances on the birds' health and survival. It seems that human-induced stress, in combination with prolonged exposure to the glacial temperatures outside igloos when birds are flushed out of their shelters, plus an increased predation risk, could explain why, in areas devoted to winter sport activities, Black Grouse populations are on average 30 to 50% less dense than in habitats with low human pressure.

A first conclusion can be drawn from these results: only the creation of suitably protected wintering refuges will enable the Alpine fauna to endure the growing pressure exerted by human activities on these vulnerable ecosystems. The Conservation Biology team at the University of Bern is currently developing spatial models that will identify geographical locations of priority concern for the creation of such refuges. These would benefit not only the endangered Black Grouse, but also other wildlife sharing its habitat.

The study was funded by the Swiss National Science Foundation and an Interreg project.

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