Bison bison bonasus, Bison bison caucasicus, Bison bison bonasus, Bison bison hungarorum.

Two genetic lines are distinguished in recent populations:

• the Lowland line (Bison bonasus bonasus) and
• the Lowland-Caucasian line (Bison bonasus bonasus and Bison bonasus caucasicus).

There are no surviving pure-bred populations of Bison bonasus caucasicus left.

Largest herbivore in Europe

European bison (Bison bonasus) is the largest herbivore in Europe. At birth, a calf's trunk is short and tall. It is only in the 8-10 months of life that those proportions undergo change, such that the thorax become as long as it is high. Throughout development, this part of the body is shorter in females than in males. At birth, bull-calves are somewhat larger than heifers. Sexual dimorphism becomes apparent from age 3 onwards, and is retained to the end of life.

Adult bulls aged 6 and over have maximum body dimensions of: 188 cm in height at the hump, 300 cm in length of the trunk, and a 280 cm circumference of the thoracic cavity. Among cows, these respective dimensions are of 167 cm, 270 cm and 246 cm.

At birth calves are quite small, weighing in at between 15 and 35 kg. In the free-ranging population of the Bialowieza Forest, body masses among adults (aged 6 and over) are of 634 kg on average in the cases of males (range 436 to 840), and of 424 among females (range 340 to 540).

A powerfull body

The powerfull body is covered in a reddish-brown coat that blends remarkably well with the animal's surroundings. The head, neck and front of the body are covered in long hair, this forming the so-called 'beard' located along the lower part of the throat and upper part of the chest. The rear part of the body is covered with short hair only, although the end of the tail again supports long hairs extending down to the level of the hock.

Best developed sense of smel

A bison's best developed sense is its sense of smell. Rutting males are adept at tracking down herds, sniffing the scent of cows that was left behind on the forest floor. The same behaviour applies where an individual becomes separated from its group for a period of time.

Fast runners

European bison are fast runners, although they are more in the nature of sprinters than long-distance operators. They ususally come to a panting stop having covered just a couple of hundred metres.

(Source: European bison, the nature monograph)

Habitat and behaviour

Optimal habitats for the European bison are deciduous and mixed forests, but the range should include about 20% of grassland habitats (meadows). In Białowieża Forest (Poland) they primarily forage in moist deciduous forests, and then in mixed coniferous forests. Forest complexes with a mosaic-like forest type arrangement (such as Białowieża and Borecka Forests, Poland) are most favourable. In fresh deciduous forest, European bison find food throughout the vegetative season.

In the Caucasus region, European bison prefer foothill forests; in summer, they feed on alpine meadows. However, considerable plasticity of European bison with regard to food means they also forage in habitats where coniferous forests predominate.

All European bison populations inhabit ranges that include open areas, such as, mown meadows, deforested feeding glades covered with grass, clear cuts and young plantations up to 10 years old. The attraction of open areas results from the fact that exploited meadows and glades provide ungulates with much more food than the same area of the forest herb layer and food is more easily available there.

The bison is active throughout the day, though the distribution of activity is affected by food supply. They feed on grasses, leaves, bark, lichens and mosses. In the summer, feeding occurs primarily in the morning and evening, and rarely at night. In the winter, two to five feeding sessions per day have been recorded, mostly in the morning and evening before midnight. Over a 24 hour period, an average of 30% of the time is spent feeding, 60% resting, and 10% moving and/or playing. Although movements are generally slow, short gallops are rarely observed. Despite their size, wisent can jump across 3 m wide streams and 2 m tall fences from a standing position. The bison is dependent on water, knocking holes in the ice in winter with their hooves to reach the liquid. Population densities are about 12 animals per 1,000 hectares in the Bialoweiza Forest in Poland, and 3-4 per 1,000 hectares in the Caucasus. Vocalizations other than short grunts or snorts are rare.

Reproduction and Groupstructure

The wisent is a gregarious (living in herds) animal, which lives in both mixed and solely-male groups. Mixed groups consist of cows, young aged 2-3 years, calves and young adult bulls. The average herd size is dependent on environmental factors, though on average, they number 8-13 animals per herd. Herds consisting solely of bulls are smaller than mixed ones, containing two individuals on average. Wisent herds are not family units. Different herds frequently interact, combine and quickly split after exchanging individuals.
Territory held by bulls is correlated by age, with young bulls aged between 5-6 tending to form larger home ranges than older males. The wisent does not defend territory, and herd ranges tend to greatly overlap. Core areas of territory are usually sited near meadows and water sources.

The rutting season occurs from August through to October. Bulls aged 4-6 years, though sexually mature, are prevented from mating by older bulls. Cows usually have a gestation period of 264 days, and typically give birth to one calf at a time.

Male bison can reach sexual maturity at ages of 15-20 months, although research suggest that such cases are rare. Today, the young 4-5 year old males in the wild population are sexually mature, but do not usually participate in reproduction for behavioural reasons, older bulls seeing to it that they are kept well away from cows on rut. Than again old bulls over 12 years are driven away from cows on rut by younger males.

Female bison of the Bialowieza Forest mated first in their 3rd and 4th years of life. Cows remain fertile into old age. In captive conditions as well as in wild populations cows are known of giving birth and succesfully rearing their calves at age of 20 years. On avergae, therefore, a cow produces 9 calves in a lifetime. European Bison have an average gestation period of 264 days. Cows calve both day and night, while standing or laying and parturition can last between one and 2 hours. Licking of the calve follows immediately from delivery, and the placenta is eaten within 4-5 hours/ The calve begins to stand 20-45 minutes after birth and will start suckling within the first hour of life.
In free-ranging population a cow about to give birth leaves the herd to deliver the calf in a safe place. After several days the mother and calf rejoin the herd. Calves are born in spring, which is the period most favourable to their subsequent development.

Bison have few predators (besides humans), with only scattered reports from the 1800's of wolf and bear predation.

Historically the bison was distributed throughout western, central, and south-eastern Europe and the Caucasus.

By the end of the 19th century, there were only two populations of European bison left in the wild: in Białowieża Forest Bison bonasus bonasus and in the western Caucasus mountains Bison bonasus caucasicus.

Bison bonasus bonasus was finally driven Extinct in the Wild in 1919, and Bison bonasus caucasicus had been extirpated by 1927.
Subsequently, the species survived only in a few European zoological gardens.

As a result of reintroductions and introductions, it now occurs in free-ranging and semi-free herds in Poland, Lithuania, Belarus, Russian Federation, Ukraine, and Slovakia. It occurred from sea level to 2,100 m in the Caucasus, and in the Carpathians it is presently found at alitutudes of up to 800 m.

The introduced Kyrgyzstan subpopulation has recently gone extinct.

Captive populations are well distributed in 30 different countries worldwide (see Pucek et al. 2004 for details).

European bison in Ukraine

Source: Kyiv Ecology & Culture Centre, Biodiversity Conservation and Protected Areas Coordinator, Ivan Parnikoza

After relatively secure Soviet times, at the end of 1990th the number of wisent's populations began to decline rapidly. Afterwards populations fully disappeared in Ivano-Frankivsk (Nadvirnyanska population), Rivne (on territory of Klevanske hunting husbandry), and Khmel'nytskiy regions (group of individuals of Volyn subpopulation which migrated from Tsumanska forest). However, thorough investigation of this adverse event was not conducted. Therefore, further development of this trend led to a sharp reduction of quantity of two major Uladivska and Bukovinska populations, and decline of Tsumanska population of Volyn region to the limits of its survival. Also we should recognize the full loss of Daniv population in Chernihiv region the real tragedy of recent years.

Dynamics of quantity of bison populations in regions of Ukraine

On the 1st of January, 2008, an amount of Ukrainian bisons according to official data was 258 heads, whereas results of independent investigations showed figures of not more than 190-230 heads.

In historical times, the European bison was widespread and presumably abundant in its native range. However, by the end of the 19th century it was close to extinction, with only two wild populations remaining. Shortly after World War I the species was Extinct in the Wild, and the captive population consisted of just 54 (29 males; 25 females) European bison with proved pedigrees, originating from 12 founder animals. The captive population subsequently increased slowly until World War II, when the species again suffered a steep decline, with the population dropping from 160 animals in 1943 to 93 in 1946.

Return of the bison

As a result of captive breeding, reintroductions and intensive conservation management, the total population of free-ranging bison now stands at c. 1,800.
A further c. 1,400 individuals live in captivity. Some captive animals are not recorded in the European Bison Pedigree Book, so this is likely to be an underestimate.

Population structure is such that approximately 60% of individuals are sexually mature. The effective population size is smaller than the total population size, because European bison are a polygynous species, so not all males have the opportunity to breed.

The free-living population increased more or less steadily from the mid-1960's to a peak of c. 2000 in the early 1990's. Following a period of decline in the mid to late 1990's, the population is once again expanding, although the potential for ongoing growth is limited by a number of factors.

Habitat degradation and fragmentation

Habitat degradation and fragmentation due to agricultural activity, forest logging, and unlimited hunting and poaching were the primary reasons for the decrease and extinction of European bison populations. Pucek has summarized the history of their extinction. Among the primary reasons for the rapid decrease of the European bison population in Białowieża Primeval Forest at the beginning of 19th century was the over-population of deer species, and the drastic reduction of natural food resources for herbivores which followed. During the period of World War I and the Russian Revolution of 1917, conflict and heavy poaching exacted a severe toll on remaining populations.

Conflict and political instability

Conflict and political instability continues to be a threat to the species in the Caucasus, where reintroduced free-living herds have suffered very severe losses (leading to extinctions) in recent years. Other current threats include lack of appropriate habitat, fragmentation of populations (and concomitant loss of genetic diversity), inbreeding depression, disease, hybridisation, and poaching.

There is little space for a large herbivore such as the European bison in Europe's contemporary ecosystems, especially in the west. The most significant limit for the enlargement of European bison populations is human population density; forestry and agricultural activity is not a limiting factor.

Genetic heterogeneity

Fragmentation and isolation of free-ranging (and captive) herds result in little or no exchange of genetic material. Small isolated populations quickly lose their genetic heterogeneity and are more vulnerable to extinction. As yet, the opportunity to reconstruct a more compact geographic range to facilitate migration of bison between herds does not exist. As a consequence of passing a dramatic bottleneck (the current population descends from just 12 founder animals), the gene pool is limited and animals are highly inbred. The average inbreeding coefficient is very high compared to other large mammals, and is equal to 44% in the Lowland line and 26% in the Lowland-Caucasian line for individuals with a full pedigree. The negative effects of inbreeding, manifested in the decline in reproduction rate, are more strongly pronounced in the Lowland-Caucasian line than in the Lowland line. Inbreeding exerts a harmful effect on skeleton growth, particularly in females, and possibly lowers the resistance of bison to disease and pathologies.

Diseases

Diseases appearing in European bison populations can bring serious threats to the whole species. It is not certain whether the species has always shown a weak resistance to disease or if immunity has declined, due to limited genetic heterogeneity. The most important disease affects the male reproductive organs and is manifested in the inflammation of the penis and prepuce, leading to diphtheroid-necrotic lesions, diagnosed as balanoposthitis. This disease was discovered at the beginning of the 1980s in Białowieża Forest; although similar symptoms had been reported earlier in Russia and Ukraine. Despite many years of study, its pathogenesis has not yet been elucidated. Other diseases that are potentially major threats to herds include foot-and-mouth disease Aphte epizooticae (to which the species is known to be sensitive), and tuberculosis .

Hybrid herds

A particular problem concerning the management of extant populations of European bison is the existence of hybrid herds, especially European × American bison hybrids living in the Caucasus. Two free-living hybrid herds have been established in the Caucasus Mountains, in close proximity to reintroduced free-living herds of the pure blood Lowland-Caucasian line. There are fears that all these animals will crossbreed, creating a mixture of various genotypes. According to Russian authors, the distances between herds are not so great, but the configuration of mountain ridges and valleys make it impossible for contact between them. There are also two small semi-free herds of European and American bison hybrids in Toksove Forest Park (St Petersburg) and the Mordovia Wildlife Reserve. Finally, poaching as a result of administrative disorders and a failure to enforce nature conservancy law threatens free-living herds of European bison in many countries.

Bison bonasus - European Bison: Historical distribution
Source: Status Report 2007 of the Large Herbivores in the Palaearctic

To add, recent map with new reintroductions elsewhere in Europe

Source: IUCN Red List for Threatened Species

• A Status Survey and Conservation Action Plan European Bison Status Survey and Conservation Action Plan for the European Bison has been published in 2004.
• Most countries in which the species occurs have national management plans.
• The European Endangered Species Programme (EEP) for zoos was established by the European Association of Zoos and Aquaria (EAZA) in 1996, and now a third of the captive population is participating in this programme.
• The European Bison Pedigree Book has been developed, which registers and publishes lists of European bison, enabling the genetic purity of the species to be maintained. 

Conservation measures recommended in the 2004 Action Plan include the following:

1. Continue captive breeding, following a coordinated programme that focuses on maintaining genetic variability. Hybridisation between existing breeding lines (Lowland and Lowland-Caucasian) should be avoided, as should hybridization between European bison and American bison Bison bison.
2. Establish a Gene Resource Bank to serve as a safeguard against loss of important genetic diversity.
3. Continue reintroductions into forests and other ecosystems. It will be necessary to link isolated subpopulations (e.g., by creating habitat corridors) and restore metapopulation function to enable the population to be self-sustaining in the long term.
4. Regulate bison populations by culling, when necessary, to prevent populations exceeding the carrying capacity of remaining habitat.
5. Manage habitat appropriately, for example by creating watering places, and cultivated meadows or feeding glades for use by other ungulates.
6. Implement and enforce stricter regulations to control poaching.
7. Continue producing the European Bison Pedigree Book, and expand its scope.
8. Implement the International Bison Breeding Centre, to coordinate reintroductions, monitoring of captive and free-ranging herds, and genetic management of particular herds.

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