Missing from the Caledonian Forest for the past 400 years, the wild boar (Sus scrofa) fulfils an essential role in the ecosystem, and its return now will aid the recovery of the forest.

Global distribution

Wild boar has the widest natural range of any ungulate, or hoofed mammal, in the world. It originally occurred from Britain and Ireland throughout all of Europe (except Scandinavia), in the Atlas Mountains in North Africa, in the Middle East and the Caucasus Mountains and through most of Central Asia to China, Taiwan and Japan. It is also found in South and Southeast Asia, from India across to Vietnam and the Indonesian islands of Sumatra and Java.

With such a huge range, there is some variation in the species, and as many as 25 subspecies have been proposed. However, the latest research indicates that there are probably only 4 subspecies, with Sus scrofa scrofa occurring in Europe, North Africa and Western Asia; S. s. ussuricus in North Asia and Japan; S. s. cristatus being found from Asia Minor to India; and S. s. vittatus occurring in Indonesia and other parts of Southeast Asia.

Outside of its natural range, the wild boar has been introduced to many other parts of the world, such as North America, Australia, New Zealand, South Africa, parts of South America and a number of Pacific Islands, including Hawaii. In addition, domesticated pigs (which are all descended from wild boar) have escaped in a number of countries and established feral populations, sometimes interbreeding with local wild populations.

Distribution in Scotland

It is likely that the wild boar originally occurred throughout most of Scotland, wherever there was suitable forest for it to live in. Fossil and archaeological remains have been found in Caithness and Sutherland, Perthshire, Fife, Berwickshire, Wigtownshire and the islands of Colonsay and Orkney. Wild boar were reduced over the centuries as the forest cover shrank, and hunting for both meat and sport also played an important part in its disappearance. An exact date for the extinction of the species in Scotland is unknown, but it is generally considered to have been in the late 16th or early 17th centuries.

In England, where the boar probably became extinct in the 13th century, animals imported from continental Europe were released in the first part of the 17th century, but they did not become successfully re-established in the wild, most likely because of persecution as agricultural pests. In the latter part of the 20th century, farmers began keeping wild boar in enclosures, and a number of animals escaped in 1987, when a severe storm blew down over 1 million trees in the south of England. Those boar, and other subsequent escapees, have become established, and today wild populations exist in Kent, East Sussex and Devon, with sightings also reported from other counties.

Feral boar are also present in various parts of Scotland, and some that escaped from Glen Dessary have spread to Glen Garry and Glenmoriston, where they have been sighted in recent years. Little is known about the population of feral boar in Scotland, but anecdotal evidence indicates that they are increasing in numbers and spreading in their geographic range. 

The wild boar is included on the IUCN (World Conservation Union) Red List of threatened Species, where it is classified as Lower Risk/Least Concern. This is the lowest category of threat on the list, and recognises that the species is in no imminent danger.

The wild boar is a member of the pig family, Suidae, and is an even-toed ungulate or artiodactyl. It is a large mammal, with an adult male weighing up to 200 kg., or occasionally more, and with a head and body length of up to 2 metres. The tail, which is usually straight, is about 25 cm. long. Female boars are about two thirds of the size of the males, although both stand about one metre in height.

A prominent feature of the wild boar is its coat of short, thick bristly hair, which can vary in colour from brown and black to grey. In western Europe, boar generally have brown coats, while in eastern Europe black coats are more common. A line of longer, upright hair grows along the spine of the boar, and this has led to their common name of razorback in the southeast of the USA, where feral pigs have given rise to a wild boar population.

Like all other even-toed ungulates, such as red deer or cattle, the wild boar has cloven hooves, which are formed by two toes, each encased in a layer of horn. In the boar's case, these toes can spread to make it easier to walk in mud or soft ground. There is a smaller toe on the outside of each of the main toes, while the fifth toe has been lost during evolution, thereby resulting in the present-day even-toed characteristic of artiodactyls.

The male wild boar develops tusks at 2 years of age, and these grow upwards from both the upper and lower canine teeth. The upper tusks are 7 – 12 cm. long, and are hollow. They are used as 'natural whetstones' for sharpening the lower tusks, which are smaller, but like the upper ones, they grow continuously.

 In the wild, the lifespan of a boar is typically 10 years, although some individuals have been known to live for 27 years. In captivity, the average lifespan is 25 years.

The wild boar is a social animal and lives in groups of 20, or sometimes more, that are called sounders. These are matriarchal and consist of two or three mature females and their recent litters or young. Adult males are usually solitary outside of the mating season. Larger groupings, of up to 50 or 100 animals are occasionally seen, and a sounder will forage together throughout a home range. The natural habitat of the wild boar is woodland, and throughout its large range, it lives in deciduous and coniferous forests, in tropical rainforests and in swamp forests.

The boar's eyesight is poor, and its eyes are only able to distinguish blue from amongst the primary colours. However, because of its largely nocturnal lifestyle, this is not necessarily a disadvantage, as blue is most easily seen in low light conditions. By contrast, the wild boar has an excellent sense of smell, and it uses its snout to search for food on the ground and in the soil. The snout is highly flexible, with a large disk of cartilage connected to muscle, and is quite powerful, enabling the boar to turn over dead logs and uproot plants. The boar also has excellent hearing, and communicates with various vocalisations. These include grunting or rumbling when content, squealing when injured or hurt, and making a snorting sound by blowing through the nose when disturbed or frightened.

The wild boar is highly intelligent, and is considered to be one of the most intelligent of all animals. In the wild it is naturally shy, and is seldom seen by humans. Although it has a fierce reputation, it is extremely rare for a boar to be aggressive towards humans; this is only likely to happen if an animal is cornered, or if a sow senses her young are threatened. Sows can be aggressive towards each other, however, when feeding or when seeking dominance within a sounder. Males are most aggressive towards each other during the breeding season, when injuries sustained in the contests over females can sometimes be fatal. A fully grown male boar is a formidable opponent when attacked, and it uses the power of its large body to charge its attacker, and its tusks to inflict serious injuries. As an adaptation to such breeding season aggression, males have developed thickened tissues at the front of their bellies, to provide protection from stabbing tusks.

The diet of the wild boar is diverse and varied, as it is an omnivorous species. Typical food includes roots and tubers, insects, worms, berries, nuts, carrion, bird eggs, lizards, snakes and small mammals such as mice. Plant material forms about 90% of the diet, and in the autumn, mast from trees such as oak and beech is a major food source. The wild boar is mainly nocturnal, and most feeding is done at night, although some foraging also takes place during the day. Most of the day time is spent sleeping, in 'day nests', which are round depressions in the ground that are sometimes lined with leaves or vegetation.

The female wild boar, or sow, has six pairs of nipples and reaches sexual maturity at 18 months of age, on average. A male may reach sexual maturity as young as 10 months old, but it is generally not until they are fully grown, at about 5 years, that males are able to compete successfully for females.

Breeding usually occurs in the autumn, in October and November, and the females have a 21 day oestrus cycle. Successful males have been documented as mating with as many as 8 females. Pregnancy lasts for an average of 115 days, and farrowing, or giving birth, happens in the spring. The sow leaves the sounder 1-3 days before giving birth, when she builds a special farrowing nest. This takes the form of a mound made from vegetation, and is built over a hollow scrape that is lined with twigs.

Litters typically contain 4-6 piglets, but can be as large as 12. The piglets weigh from 750 gm to 1 kg at birth, and remain in or close to the nest for 4-6 days, before the sow and her young rejoin the sounder. Rooting behaviour begins after a few days and the piglets will eat solid food after two weeks. Piglets will sometimes cross-suckle from other lactating sows in the sounder, and weaning takes place at between 3 and 4 months of age.

The piglets have a characteristic striped pattern on their coats, with longitudinal stripes of light brown and cream, and this gives way to adult colouration at about 6 months old. Mortality is high amongst the young, mainly due to predation.

Because of its large size and its frequent rooting for food, the wild boar has a significant effect on the forest floor where it lives. In particular, by disturbing the soil, it creates ideal conditions in the Caledonian Forest for the germination of Scots pine (Pinus sylvestris) seedlings, as they thrive best in exposed mineral soil. However, other plants also benefit from this rooting behaviour, through the provision of a good growing medium for seedlings, and in some cases, the dispersal of the seeds themselves, which are sometimes pushed into the soil by the boar's snout as it roots around.

Ground disturbance is of course also destructive for some plants, and Britain's famous bluebell woods are attributed by some people to the absence of wild boar. The theory is that in other parts of Europe, the rooting of wild boar prevents the mass displays of bluebells (Hyacinthoides non-scripta) that grace many of our woods in May and early June.

Another species whose abundance may be related to wild boar is bracken (Pteridium aquilinum). This rhizomatous fern spreads by underground runners, or rhizomes, from which the fronds grow each year. The fronds are toxic to animals, so because of preferential grazing on other more palatable species, bracken has taken over in many places and forms dense, uniform patches, which shade out seedlings of other plants. Wild boar, however, dig up and eat the bracken rhizomes, so they may have been a control on bracken before they were exterminated in the UK. The Guisachan Wild Boar Project is seeking to quantify and document the effect of wild boar in controlling and removing bracken from an area of native pine forest.

Predators of the wild boar in Europe include the wolf (Canis lupus), brown bear (Ursus arctos) and the lynx (Lynx lynx), with young animals being taken in most instances. However, the wild boar also benefits from the presence of predators, as it will feed on carrion left from lynx kills, for example, and boars have even been known to drive a lynx off its fresh kill, so that they could feed on it themselves. Elsewhere in their range, wild boar are preyed upon by tigers (Panthera tigris), leopards (Panthera pardus) and crocodiles (Crocodylus spp.).

Like all large mammals, the wild boar is a host for a number of parasites, including internal or endoparasites such as tapeworms (Taenia solium), whipworms (Trichuris spp.) and nematodes ( Ascaris sp. ). External or ectoparasites include the pig louse (Haematopinus suis) and ticks (Ixodes ricinus), and in Spain a tick which had fed on a wild boar was found to be carrying one of the bacteria (Borrelia afzelli) that cause Lyme disease. To rid itself of external parasites, the wild boar regularly visits puddles or wet ground, where it will wallow in the mud. In this regard, it also benefits from the attention of the magpie ( Pica pica ), which will perch on a boar's back and eat ticks and other parasites.

The wild boar has been missing from the Caledonian Forest for at least the past four centuries, during which time the absence of its essential ecological role has contributed to the overall decline of the forest. The return of the wild boar to its rightful place in the ecosystem now is a vital step towards the recovery of the forest to full health and diversity.