Figure 2.

Stress level faced by wild free-ranging black grouse, measured as the relative concentration of faecal corticosterone metabolites (mean+s.e., in nmol kg⁻¹ of dry material) in droppings collected from individual snow burrows. Data are presented as percentage, with the mean value of the control reference set at 100% (i.e. day before initial flushing in the experiment, or habitat with null or limited disturbance in the comparative approach). (a) Results of a disturbance experiment with three radiomonitored males that were experimentally flushed in winter, once a day over four successive days. Faecal corticosterone metabolite levels increased significantly from control day 0 throughout to day 3 of experiment (linear mixed model), stemming mainly from a difference between the control and the experimental days (χ₁²=7.9, p=0.005), and not from differences among experimental days (χ₂²=0.3, p=0.86); (b) Faecal corticosterone metabolite concentrations in the droppings collected from 32 sites spread across SW Switzerland (totalling 132 igloo samples) with various levels of disturbance by skiers and snowboarders (sample size at column foot), after correction for a seasonal effect. Stress hormone concentrations differed significantly between sites with no or limited human disturbance versus sites with either moderate or high disturbance; the latter two categories did not differ between each other. ^*p<0.05.