Common raccoon dog

Canid indigenous to East Asia

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The common raccoon dog (Nyctereutes procyonoides), also called the Chinese or Asian raccoon dog to distinguish it from the Japanese raccoon dog, is a heavy-set, fox-like canid native to East Asia. Named for its raccoon-like face markings, it is most closely related to foxes. Common raccoon dogs feed on many animals and plant matter, and are unusual among canids (dogs, foxes, and other members of the family Canidae) in that they hibernate during cold winters and can climb trees. They are widespread in their native range, and are invasive in Europe where they were introduced for the fur trade. The similar Japanese raccoon dog (Nyctereutes viverrinus, the tanuki), native to Japan, is the only other living member of the genus Nyctereutes.

The closest relatives of the common raccoon dogs are the true foxes, not the raccoon, which is one of the musteloids, and not closely related. Among the Canidae, the common raccoon dog shares the habit of regularly climbing trees only with the North American gray fox, which is neither a true fox nor a close relative of the common raccoon dog.

Due to the fur trade, the common raccoon dog has been widely introduced in Europe, where it has been treated as a potentially hazardous invasive species. In Scandinavia, it is called "marten-dog" (Swedish: mårdhund, Norwegian and Danish: mårhund). In Europe, since 2019, the common raccoon dog has been included on the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.

Description

Common raccoon dog skulls greatly resemble those of South American foxes, particularly crab-eating foxes, though genetic studies reveal they are not closely related. Their skulls are small, but sturdily built and moderately elongated, with narrow zygomatic arches. The projections of the skull are well-developed, with the sagittal crest being particularly prominent in old animals.

Reflecting their omnivorous diets, common raccoon dogs have small and weak canines and carnassials, flat molars, and relatively long intestines – (1.5–2.0 times longer than other canids). They have long torsos and short legs. Total lengths can range from 45 to 71 cm (18 to 28 in). The tail, at 12 to 18 cm (4.7 to 7.1 in) long, is short, amounting to less than a third of the animal's total length and hangs below the tarsal joints without touching the ground. The ears are short and protrude only slightly from the fur.

Weights fluctuate according to season: in March they weigh 3 kg (6.6 lb), while in August to early September males average 6.5–7 kg (14–15 lb), with some individuals attaining a maximal weight of 9–10 kg (20–22 lb). Specimens from Japanese and Russian studies have been shown to be on average larger than those from Chinese studies.

The winter fur is long and thick with dense underfur and coarse guard hairs measuring 120 millimetres (4.7 in) in length. The winter fur protects common raccoon dogs from low temperatures ranging down to −20 to −25 °C (−4 to −13 °F). It is of a dirty, earth-brown, or brownish-grey colour with black guard hairs. The tail is darker than the torso. A dark stripe is present on the back, which broadens on the shoulders, forming a cross shape. The abdomen is yellowish-brown, while the chest is dark brown or blackish. The muzzle is covered in short hair, which increases in length and quantity behind the eyes. The cheeks are coated with long, whiskery hairs. The summer fur is brighter and reddish straw-coloured.

A rare white colour type occurs in China. They can also come in a yellow colour.

Ecology

Diet

Common raccoon dogs are omnivores that feed on insects, rodents, amphibians, birds, fish, reptiles, mollusks, crabs, sea urchins, human garbage, carrion, and eggs, as well as fruits, nuts, and berries. Among the rodents targeted by common raccoon dogs, voles seem to predominate in swampy areas, but are replaced with gerbils in flatland areas such as Astrakhan. Frogs are the most commonly taken amphibians; in the Voronezh region, they frequently eat fire-bellied toads, while European spadefoot toads are usually taken in Ukraine. Common raccoon dogs are able to eat toads that have toxic skin secretions by producing copious amounts of saliva to dilute the toxins. They prey on waterfowl, passerines, and migrating birds. Grouse are commonly hunted in their introduced range, and many instances of pheasant predation are recorded in the Ussuri territory.

Common raccoon dogs eat beached fish and fish trapped in small water bodies. They rarely catch fish during the spawning season, but eat many during the spring thaw. In their southern range, they eat young tortoises and their eggs. Insectivorous mammals hunted by common raccoon dogs include shrews, hedgehogs, and, on rare occasions, moles and desmans. In the Ussuri territory, large moles are their primary source of food. Plant food is highly variable, and includes bulbs, rhizomes, oats, millets, maize, nuts, fruits, berries, grapes, melons, watermelons, pumpkins, and tomatoes.

Common raccoon dogs adapt their diets to the season; in late autumn and winter they feed mostly on rodents, carrion, and feces, while fruit, insects, and amphibians predominate in spring. In summer they eat fewer rodents, and mainly target nesting birds, fruits, grains, and vegetables.

Predators

Wolves are the main predators of common raccoon dogs, killing large numbers of them in spring and summer, though attacks have been reported in autumn, too. In Tatarstan, wolf predation can account for more than half of dog deaths, while in northwestern Russia, it can amount to almost two-thirds. Red foxes kill common raccoon dog pups, and have been known to bite adults to death.

Both foxes and European badgers compete with common raccoon dogs for food, and have been known to kill them if common raccoon dogs enter their burrows. Eurasian lynxes rarely attack them. Birds of prey known to take raccoon dogs include golden eagles, white-tailed eagles, goshawks, and eagle owls.

Behaviour

Reproduction and development

The mating season begins from early February to late April, depending on location. Common raccoon dogs are monogamous animals, with pair formations usually occurring in autumn. Captive males, however, have been known to mate with four or five females. Males will fight briefly, but not fatally, for mates. Copulation occurs during the night, or at dawn, and typically will last 6–9 minutes. Estrus lasts from a few hours to six days, during which females may mate up to five times. Females enter estrus again after 20–24 days, even when pregnant.

The gestation period lasts 61–70 days, with pups being born in April–May. Litter sizes typically consist of 6–8 pups, though 15–16 pups can be born in exceptional cases. First-time mothers typically give birth to fewer pups than older ones. Males take an active role in raising the pups. This male role is very significant, as demonstrated by early releases in 1928 of pregnant females without males, resulting in very limited success at introduction, while later releases of pairs from 1929 until the 1960s resulted in the common raccoon dog's now-extensive introduced European range.

At birth, pups weigh 60–110 g (2.1–3.9 oz), and are blind and covered in short, dense, soft wool lacking guard hairs. Their eyes open after 9–10 days, with the teeth erupting after 14–16 days. Guard hairs begin to grow after 10 days, and first appear on the hips and shoulders. After two weeks, they lighten in colour, with black tones remaining only around the eyes. Lactation lasts for 45–60 days, though pups begin eating food brought to them as early as the age of three weeks to one month. They reach their full size at the age of 4.5 months. Pups leave their parents in late August–September. By October, the pups, which by then resemble adults, unite in pairs. Sexual maturity is reached at 8–10 months. Their longevity is largely unknown; animals 6–7 years of age have been encountered in the wild, while captive specimens have been known to live for 11 years.

Hibernation

Common raccoon dogs are the only canids known to hibernate. In early winter, they increase their subcutaneous fat by 18–23% and their internal fat by 3–5%. Animals failing to reach these fat levels usually do not survive the winter. During their hibernation, their metabolism decreases by 25%. In areas such as Primorsky Krai and their introduced range, common raccoon dogs hibernate only during severe snowstorms. In December, their physical activity decreases once snow depth reaches 15–20 cm (5.9–7.9 in), and limit the range from their burrows to no more than 150–200 m (490–660 ft). Their daily activities increase during February when the females become receptive, and when food is more available.