The European bison (Bison bonasus) is a flag example of a successful recovery of a big ungulate species. It went extinct in the wild nearly 100 years ago due to mass poaching during WWI in the Białowieża Forest. Thanks to immense international effort, single remnants of the species from zoos and collections enabled its recovery and also their re-introduction into the forest, years later. Since the recovery, the total number of the species has grown up to 6000 individuals, the majority of which are in free-living herds.
However, the bottleneck that European bison went through left a dramatic mark on its genetic diversity and thus on its evolutionary potential. European bison have one of the least favourable genetic parameters ever reported for wildlife and extremely high level of inbreeding. The latter is associated with a series of developmental and reproductive disorders. Six to eight percent of males every year are affected by an incurable and lethal genetically-conditioned disease of male reproductive organs (posthitis). High genetic homogeneity of a species is a serious potential threat in case of emerging a new risk factor. The substantial threat for the European bison is also, most generally speaking, inapropriate management of the population i.e. unreasonable culling, excessive winter feeding, inadequate locations for new herds, rapid animal movements and lack of genetic monitoring of the transported animals.
The experience of the European bison reintroduction could be a reliable reference of potential ups and downs for any other megafauna species recovery.