European Bison - Miscellanea

Miscellanea

European bison have lived as long as 30 years in captivity, although in the wild their lifespan is shorter. Productive breeding years are between four and 20 years of age in females, and only between six and 12 years of age in males. Wisent occupy home ranges of as much as 100 km2 (40 sq mi) and some herds are found to prefer meadows and open areas in forests.

European bison can cross-breed with American bison. The products of a German interbreeding program were destroyed after World War II. This programme was related to the impulse which created the Heck cattle. The cross-bred individuals created at other zoos were eliminated from breed books by the 1950s. A Russian back-breeding program resulted in a wild herd of hybrid animals, which presently lives in the Caucasian Biosphere Reserve (550 individuals in 1999).

There are also wisent-cattle hybrids, similar to beefalo in North America. Cattle and European bison can hybridise fairly readily, but the calves cannot be born naturally (birth is not triggered correctly by the first-cross hybrid calf, and they must therefore be delivered by Caesarian section). In 1847, a herd of wisent-cattle hybrids named żubroń was created by Leopold Walicki. The animals were intended to become durable and cheap alternatives to cattle. The experiment was continued by researchers from the Polish Academy of Sciences until the late 1980s. Although the program resulted in a quite successful animal that was both hardy and could be bred in marginal grazing lands, it was eventually discontinued. Currently the only surviving żubroń herd consists of just a few animals in Białowieża Forest, Poland and Belarus.

The modern herds are managed as two separate lines – one consisting of only Bison bonasus bonasus (all descended from only seven animals) and one consisting of all 12 ancestors including the one Bison bonasus caucasicus bull. Only a limited amount of inbreeding depression from the population bottleneck has been found, having a small effect on skeletal growth in cows and a small rise in calf mortality. Genetic variability continues to shrink. From five initial bulls, all current European bison bulls have one of only two remaining Y-chromosomes.