## 4 Discussion
### Conclusions and Further Research  
Spatial requirements of capercaillie are large, a lively population of capercaillie might require around 250 km\({}^{2}\)[55]. Moreover, number and size of suitable habitat patches and the distance between them determine capercaillie occupancy and dispersal [15; 17]. The observed shift in capercaillie altitudinal distribution could therefore be restricted to our study area. In fact, a possible drawback of our study is the limited area investigated and the relatively small number of surveyed plots. Nevertheless, models of this species built with regional-scale data may not be appropriate for understanding habitat preferences and the effects of their changes [56], and proposing restoration actions at the stand scale. Periodic stand-level monitoring would thus improve the understanding of regional trends, because we observed that the variables with the highest predictive powers changed across time.  
In addition to what was observed in our study, other factors may have played a role. For example, changes in ungulate populations might also influence habitat use by capercaillie [57]. Human disturbance might be another contributing factor. Tourism and forest management [19; 46] at lower altitudes could have emphasized the effects of land cover changes pushing capercaillie upwards in the post-breeding season. Lastly, being a key factor in other European contexts, increased predation at lower altitudes may have been driven by habitat cover changes [18; 58; 59] and capercaillie mobility might have been an adaptation to avoid predation [13].  
This study focused on data recorded in two years during one season. However, while land use changes likely played a major role, it must be emphasized that additional studies over longer time-spans are needed to detect consistent trends and exclude short-term phenological effects related to the summer growing season. Additional research should focus on linking the observed altitudinal shift to other likely drivers.  
Conceptualization, S.M.M. and T.S.; Methodology, S.M.M. and T.S.; Formal Analysis, M.D. and T.S.; Investigation, F.D., S.M.M. and T.S.; Writing-Original Draft Preparation, A.P., T.C., T.S.; Writing-Review & Editing all authors; Visualization, A.P., T.C., M.D., T.S.  
The 2001 survey was funded by the Autonomous Province of Trento within a service contract with S.M.M., M.D. was supported by a postdoctoral research fellowship \"Grant\" (Dept. TESAF Decree no. 36/Protocol no. 1006/2011), T.C. was supported by a postdoctoral research fellowship (Dept. TESAF Decree no. 35/Protocol no. 2010/2017), A.P. was supported by a PhD grant from the Fondazione Cariparo.  
Figure 6: Distribution of land cover types in the Scanuppia Natura 2000 site. The altitudinal distribution of capercaillie in 2011, currently centered at 1620 to 1750 m a.s.l., is closer than in 2001 to the dwarf mountain pine scrub, which is unsuitable to capercaillie (source: Provincia Autonoma di Trento, Servizio Sistemazione Montana, 2001).  
**Acknowledgments:** The authors thank the Autonomous Province of Trento for supporting this study and three anonymous referees for the comments received on previous versions of this manuscript.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, nor in the decision to publish the results.