The European bison ( Bison bonasus ), also known as the wisent, is a mammal in the family Bovidae . It is one of two extant species of bison . Having been hunted to extinction in the wild by the early 20th century, the European bison was reintroduced to the wild in various European countries by the 2010s, following captive breeding programmes. It is the heaviest wild land animal in Europe, and individuals in the past may have been even larger than their modern-day descendants. The largest bulls of the species have a mass of up to 1,000 kilograms (2,200 lb). The European bison is a herd animal, which lives in both mixed and solely male groups. Mixed groups consist of adult females, calves, young aged two to three years, and young adult bulls. A typical herd numbers around eight to thirteen animals on average. This male European bison was photographed in the Białowieża Forest , Poland.