What hampers European bison’s movements? A case study from the Carpathians

The success of every reintroduction project strongly depends on a proper identification of suitable habitats within a species' former range (IUCN/SSC 2013). However, quite frequently, purportedly suitable habitat patches become quickly abandoned after release, or introduced animals move into different directions than expected (e.g., Hirzel et al. 2004; Müller et al. 2014). Therefore, a-priori habitat suitability modeling coupled with connectivity and movement analyses can be an important tools to avoid such pitfalls.
We use the example of European bison (Bison bonasus L.) in the Carpathians to understand drivers of post-release species dispersal. Wisent was extirpated from the Carpathians during the 18th century. First reintroductions in the region were undertaken independently from each other in Poland and Ukraine in the early 1960s, and a coordinated restitution project involving five countries (Poland, Slovakia, Ukraine, Romania and Hungary) was initiated later in the 1990s (Perzanowski & Olech 2013). The reintroduced animals, against prior expectation, have not colonized areas along the Carpathian ridge, but instead have expanded their range almost exclusively towards the north, gradually entering into the area dominated by agriculture and human settlements (Perzanowski et al. 2008).
We predicted bison habitat suitability in the northeastern Carpathians using maximum entropy modeling. Then, to determine the level of connectivity of the bison habitat patches, and to map movement barriers in the landscape, we used a hybrid approach combining least-cost modeling, electrical circuit theory, and centrality analyses (Ziółkowska et al. 2016).
Although we identified a network of suitable wisent habitat patches along the Carpathian ridge, the functional connections between them were limited due to a number of major barriers to movement. Main movement barriers and bottlenecks within corridors were associated to roads restricting wisent movement in the west-east direction (i.e., the international road E371 connecting Poland and Slovakia, and the provincial roads 892, 893, and 897 in Poland), therefore explaining the surprising dispersal behavior of wisents since their reintroductions in the 1960s and 1980s.
To avoid future conflicts between wisents and people, and to achieve the long-term goal of a viable European bison metapopulation in this region, conservation action should focus on establishing connectivity between habitat patches through the creation and legal protection of corridors and wildlife passages, which would benefit Carpathian wildlife in general.

Acknowledgments
We acknowledge support by the Polish National Science Centre, project 2011/03/D/ST10/05568 (EZ, KO); the Doctus program (EZ); the Ministry of Science and Higher Education in Poland, grant no. 263/E-338/STYP/7/2012 (KO); the Einstein Foundation Berlin, grant no. EJF-2011-76 (TK); and the State of Berlin (BB, via an Elsa-Neumann-Scholarship).