European Bison (Wisent)

(Bison bonasus)

Population

7,500

Herd size

8-15 animals

Average pregnancy

8 2/3 months

Average height

1.65-1.90 m

Weight

300-1000 kg

Lifespan

18-30 years

Species profile

The European bison is the largest native herbivore in Europe. It has a dark- or reddish-brown coat, short, angular horns, and a large, muscular hump between the shoulder blades. Adult males can grow to a height of 1.9 metres, reach a length of 3 metres and weigh up to 1000 kg. Due to its large size, the bison has a significant impact on its ecosystem, and has therefore been classified as a keystone species (defined as a species which plays a crucial role within an ecosystem and on which other species may depend for their survival). Its behaviours, including browsing and trampling, help to create a mosaic-type landscape high in biodiversity and resilient to climate change.

 

 

 

 

 

History

The Bison genus most probably originates from southern Asia. In the late Pliocene era and the early Pleistocene, about 2.6 million years ago, bison larger than their present day descendants roamed the temperate regions of Asia and Europe. Somewhere between 195,000 and 135,000 years ago, they crossed the Bering Strait to North America. This led to the emergence of the American bison (Bison bison) and the European bison (Bison bonasus), which are both closely related and cross-fertile. A third species, the steppe bison (Bison priscus), was also present during the Pleistocene, ranging from Europe to North and Central America, until it became extinct at the end of the last ice age, some 10,000 years ago.

The evolutionary history of the European bison before the current geological era is largely unknown. However, for the last 12,000 years the species has been distributed throughout western, central and south-eastern Europe. This range has been reduced and fragmented over the centuries, in large part due to hunting and habitat destruction by humans, leading to the isolation of subpopulations and a subsequent reduction in genetic diversity and resilience.

By the beginning of the 20th century, the European bison was on the edge of extinction. Only two populations remained in the wild: B. b. bonasus, in Poland’s Białowieża Forest, and B. b. caucasicus, in the Russian Caucasus mountains. These populations became extinct in 1919 and 1927 respectively, and the species survived only in zoological gardens.

All living European bison descend from 12 individuals, who were the only purebreds remaining in captivity. Two breeding lines derive from these founders: the Lowland line (B. b. bonasus), descended from seven bison of pure Polish ancestry and classified as ‘vulnerable’ on the IUCN Red List (the world’s largest source of information on the global extinction risk of known species), and the ‘endangered’ Lowland-Caucasian line (B. b. bonasus and B. b. caucasicus), descended from these and four other Polish bison, and a Caucasian bull. The population of the Lowland line is still increasing, while that of the Lowland-Caucasian line has been declining since the 1990s.

Since the first European bison were released into the Białowieża Forest in 1954, other reintroductions have been carried out across the continent. Today, the free-ranging herds of the species are found primarily in eastern Europe. The global population of European bison now stands at over 6,000, the majority of which are free-living.

Behaviour and Ecology

European bison roam in open or semi-open grasslands and seek food and shelter in forests. Their ideal habitats are deciduous and mixed forests, particularly those comprising a mixture of tree-cover and open glades. They feed primarily on grasses and herbs, which constitute two-thirds of their diet, as well as on trees and shrubs. The average diet consists of over 50 grass species and 10 tree and shrub species. Their preference for particular plant species varies with the region and the season; for example, coniferous forests become a primary food source in winter.

In the vegetative season, almost two-thirds of each day is spent feeding, and the remainder is mostly devoted to resting. The time given to these behaviours is reversed in the winter, so that most of the day is spent resting and only a few hours eating. The amount of food that a bison consumes per day correlates with their age; calves up to one year old will eat approximately 9 kg daily, while some adults, aged 6 and over, can eat up to 60 kg. Unlike feeding, drinking is irregular and infrequent. In the snow-free period, bison drink from streams, small rivers and permanent water reservoirs; in the winter, they break up frozen forest soil, crush ice on streams, and drink snow-water.

The home ranges of herds overlap with each other and include core, central areas where much of their activity takes place, such as meadows or watering places. Groups of bison typically contain between 10 and 20 individuals. These groups mix and exchange members frequently, and their size and structure vary in response to seasonal and behavioural factors; for example, most bulls are solitary and join herds only for the rutting season, which runs from August to October. In winter, the movement of populations is greatly restricted by long-lasting deep snow-cover and low temperatures.

A European bison develops fastest during its first year of life. From the age of 2, growth continues at a slower rate, until the age of 5 or 6. Physical and behavioural differences between genders (also called sexual dimorphism) become fully apparent at the age of 3 and remain until the end of life. Males reach sexual maturity by the age of 4, but only engage in reproductive activity between the ages of 6 and 12. Females will give birth to their first calf around the age of 4 and continue to bear offspring every two years until the end of life. The average life expectancy for a free-living bull is 15 years, and for a female it is 24 years. Animals living in captivity tend to be larger and live longer than those in the wild.

Conservation

One of the greatest threats faced by the European bison is posed by excessive inbreeding. Inbreeding is the result of the isolation of bison populations due to habitat fragmentation, and can have harmful effects on their growth and immunity. The contribution and retention of the original founder genes is also decreasing over time, leading to a continued loss of genetic diversity and threatening the survival of the species.

Other obstacles to the conservation and expansion of the species include a lack of space for reintroductions, particularly in western Europe, the continued destruction and fragmentation of habitat due to human activity, the absence of a unified administrative body responsible for the management of populations, the lack of a clearly established legal status for the species, poaching, and diseases, such as foot-and-mouth disease and balanoposthitis (affecting the male reproductive organs).

In order to ensure the survival of the species, the establishment of programmes to save genetic diversity, protect health and extend herds is recommended. Research into bison behaviour towards human activities, optimal habitat and diet, and genetic variability is also required.

Copyright: Alexander Coughlan, B.A.