Climate and land cover changes are pushing capercaillie towards its habitat limits: a case study with management implications

Capercaillie (Tetrao urogallus L.) is a territorial Galliform species, which is known to prefer mature stands of conifers with well-spaced-trees. To foster the presence of the Capercaillie it is very important that a vigorous understory of ericaceous species (in particular, Vaccinium myrtillus L.) provides for nutritious food and cover. Capercaillie is a protected species included in Annex I of the European Directive 2009/147/EC (Birds Directive), and it is considered an umbrella species. The populations of the southern distributional range experienced, recently, a declining trend, which needs to be further analysed. The aim of the present study is to identify and assess the change in summer Capercaillie habitat that occurred in the period between 2001 and 2011 within the alpine Scanuppia Regional Natural Reserve, in Trento, Italy. The area is dominated by Spruce (Picea abies (L.) Karsten) forest in occasional association with Silver fir (Abies alba Miller), Larch (Larix decidua Miller), and Beech (Fagus sylvatica L.). Together with predominant coniferous forests, mixed stands and open pastures create a mosaic of different landscapes, which are of importance for the Capercaillie to thrive. Information about Capercaillie presence and the characteristics of the habitat have been collected through a systematic sampling. Such a technique was repeated in 2001 and 2011, and it was based on the selection of a number of 10-m radius circular plots located along the contour lines between 1,500 and 1,800 m. At the plot level, the structure of the stands and the vegetation composition characteristics have been studied, while the presence/absence of Capercaillie was recorded through the detection of droppings. Our results show that, in general, the overall population of the Scanuppia Regional Natural Reserve remained unchanged over the surveyed period in terms of abundance of individuals between the two years of survey. However, the results of our study also show that an altitudinal shift of the Capercaillie distribution occurred at an annual rate of 6.5 meters per year in the area of interest- Compared to literature, this has been quite a fast phenomenon. Compared to the results of 2001, altitude had a remarkably higher influence in 2011. According to our analysis, the forest type played a fundamental role in influencing the presence of Capercaillie in both years, clearly much higher than the factor related to the stand structure development stages. Specifically, the cover of spruce in the tree layer was positively affecting the species, while the presence of pole stands showed to be a deterrent for the bird’s settlement. In general, habitat variables seemed to be more significant for determining the presence of Capercaillie at the lower altitudes, at least in 2001. Despite our results, it is important to underline that the selection of habitat towards the upper limit of forests might be linked not only to land cover change, but also to increased summer temperatures, or to a combination of both drivers. This study highlights the need for further research to disentangle the potential factors explaining the observed changes in Capercaillie habitat selection in relation to forest management.