The winter roosting and diet of Black Grouse Tetrao tetrix in the north-western Italian Alps

The factors influencing the selection of Black Grouse Tetrao tetrix winter roost sites and choice of roosting strategy (open-air roosts vs. snow burrows, or ‘igloos’) were assessed in the Alps, including the influence of winter diet, snow conditions and habitat at different scales. Of 337 roosts detected, 31 % were igloos and 69 % were open-air roosts. At the larger scale (30 × 30 m), ground curvature, altitude, slope, southerly aspect and mountain pine Pinus montana uncinata cover were positively correlated with roost presence. At the smaller scale (10 m radius), roost presence was positively correlated with a northerly aspect, cover of green alder Alnus viridis, and a low cover of vegetation downslope from the roost. Roosting strategy was related to temperature and snow conditions (with more igloos when snow depth was greater, but fewer igloos when a hard snow crust had formed). The winter diet of the Black Grouse mostly comprised mountain pine needles (84 % of droppings). The results suggest that a range of factors influence choice of roost site, including predator avoidance, food availability and topography. The latter showed contrasting effects at different scales, suggesting that Black Grouse select colder sites (with deeper snow) within warmer areas (energetically more favourable). Management to encourage the mountain pine, whilst maintaining scattered green alder in the understorey, is likely to improve Black Grouse winter habitat quality. Choice of roosting strategy is, however, dictated by weather conditions. If the reduction in precipitation and snow cover continues as forecast, open-air roosting might be more frequent in the future. However, open-air roosting might increase predation risk, which could be deleterious for the species’ conservation.