Range expansion of three invasive alien mammals in Bulgaria

We report the changes in the distribution of three alien mammal species in Bulgaria, the coypu Myocastor coypus, the muskrat Ondatra zibethicus, and the raccoon dog Nyctereutes procyonoides after their entry into Bulgaria in the fifties and sixties of the last century. The data has been summarised from field surveys, reviews from scientific literature, analyses from official databases of national institutions and organizations, databases compiled from volunteers and hobbyists, etc. After its introduction in 1953, M. coypus rapidly spread in Bulgaria and there are more than 417 records of the species. Today it is the most widespread invasive mammal in the country. O. zibethicus was introduced in 1956, and is known from only 22 records. However, this species was able to cross the physicogeographic barrier of the Balkan Mountains in 2007, which is a strong evidence for its invasive capabilities in the territory. The first observations of N. procyonoides were reported in 1968. There are currently 75 records of the species coming from almost the entire territory of Bulgaria. The majority of the records (77.4%) are between sea level and 199 m a.s.l. and 56% of them are in national protected areas. The most frequently observed negative impacts are described and recommendations are made for further study and reducing the populations of the invasive mammals.