The struggle to rescue European bison (B. Bonasus) from extinction began about 80 years ago, after World War. Although the species became extinct in the wild, a few specimens remained in some European zoos. The first reintroduction of this species to forest ecosystems began in Białowieża, in 1952: International Bison Defense Company (CIDB) has managed to reintroduce 12 specimens in the primeval forest. It is estimated a current population of 6,000 specimens (EBPB 2016), therefore, these are in danger of total extinction; In addition, its low genetic diversity, the result of consanguinity, makes these animals especially vulnerable.
In 1966 the UN included the European bison in its <<list of protected animals>>. Today, only 2,500 Bonasus live in large areas managed as controlled-freedom, the rest are in zoos or small centers.