Climate change has influenced a range of species across the globe. Yet, to state a noted decline in the abundance of a given species as a consequence of a specific environmental change, for instance, spatially explicit long-term data are a prerequisite. This study assessed the extent to which prolonged snow-free periods in autumn and spring have contributed to the decline of the willow grouse, the only forest grouse changing into a white winter plumage. Time-series data of willow grouse numbers from summer surveys across the study area were integrated with local data on weather (snow cover), mammalian predator abundance and hunting intensity. Modelling was conducted with a hierarchical Bayesian Poisson model, acknowledging year-, area-and location-specific variability. The results show that while willow grouse numbers had decreased continuously across the study landscapes, the decrease was accelerated at the sites where, and during the years when the preceding April was the most snow-free. This indicates a mismatch between the change into a white winter plumage and the presence of snow, turning the bird into an ill-camouflaged prey. The results thus also confirm past hypotheses where local declines of the species have been attributed to prolonged snow-free periods. Across our study area, autumns and springs have become more snow-free, and the trend has been predicted to continue. Thus, in addition to conservation actions, the future of a species such as the willow grouse is also dependent on its ability to adapt to the changed environmental conditions.

Annual, nationwide monitoring of the grouse (hunted tetraonid birds) began in Finland at the beginning of the 1960s followed by systematic counts of mammal snow tracks in the late 1980s. The wildlife triangle scheme, started in 1989, gathers game monitoring data throughout the country. The system is based on a large network of triangles made up of 4 km transects (totaling 12 km per triangle) covering the entire country. The program involves an astonishing amount of fieldwork: about 10 000 km of transect line (about half of the established transects) is studied during every summer and winter count. The riistakolmiot.fi internet service was launched for the 2014 late-summer count. Via the internet, trained hunters can record their observations in a database and follow the progress of the count during the fieldwork period. In the public section of the website, anyone can view the results of ongoing counts. The internet service speeds up the collection of observations, simplifies the storing of data, and assists in preparing and sending the summary reports. Data provided by the wildlife triangle scheme are utilized by the European Union, the Ministry of Agriculture and Forestry, and other game administrative organizations, as well as hunting clubs and the general public. Annual results of the late-summer monitoring procedure are used immediately when deciding on the restrictions to the forthcoming grouse hunting season, which is due to begin just a few weeks later.

No abstract