The Southern birch mouse Sicista subtilis
(Pallas, 1773) is one of the rarest and least known small mammal species in Europe. Populations of this endangered species have suffered increasing fragmentation and isolation over the recent past. The distribution of this unique rodent has become restricted to a small part of its historical range, and the remaining habitats are also highly fragmented and mostly located on suboptimal terrain. European occurrences of the species have been reported in Poland (Baraniak et al. 1998), Romania and Bulgaria (Ausländer and Hellwing 1957), Serbia (Tvrtković and Dzukić 1974, Ham et al. 1983), Russia (Sokolov et al. 1986, Kovalskaya and Federovich 1997, Kovalskaya et al. 2000), Ukraine (Selyunina 1994, Zagorodniuk 2005), Slovakia (Demeter and Obuch 2004) and Hungary (Cserkész and Gubányi 2008). According to G. Demeter (pers. comm.) who found the Slovakian specimens in 20-30 year old owl pellets, this species probably does not occur in this region any more. It is extinct in Austria (Pucek 1999). In the coastal region of Black Sea the population of this mouse is not decreasing (Selyunina 2003) which is unique in Europe. Its recent status is unknown in Romania, Bulgaria and Serbia.