# Water deer

The water deer (Hydropotes inermis) is a small deer species native to Korea and China. Its prominent tusks, similar to those of musk deer, have led to both subspecies being colloquially named vampire deer in English-speaking areas to which they have been imported. It was first described to the Western world by Robert Swinhoe in 1870.

## Taxonomy

There are two subspecies: the Chinese water deer (H. i. inermis) and the Korean water deer (H. i. argyropus). The water deer is superficially more similar to a musk deer than a true deer; despite anatomical peculiarities, including a pair of prominent tusks (downward-pointing canine teeth) and its lack of antlers, it is classified as a cervid. Yet its unique anatomical characteristics have caused it to be classified in its own genus (Hydropotes) as well as historically its own subfamily (Hydropotinae). However, studies of mitochondrial control region and cytochrome b DNA sequences placed it near Capreolus within an Old World section of the subfamily Capreolinae, and all later molecular analysis show that Hydropotes is a sister taxon of Capreolus.

## Etymology

The genus name Hydropotes derives from the two ancient Greek words ὕδωρ (húdōr), meaning "water", and πότης (potḗs), meaning "drinker", and refers to the preference of this cervid for rivers and swamps.
The etymology of the species name corresponds to the Latin word inermis meaning unarmed, defenceless—itself constructed from the prefix in- meaning without and the stem arma meaning defensive arms, armor—, and refers to the water deer's lack of antlers.

## Habitat and distribution

Archeological studies indicate water deer was once distributed among much broader range than currently during the Pleistocene and the Holocene periods; records have been obtained from eastern Tibet in the west, Inner Mongolia and northeastern China in the north, southeastern Korean Peninsula (Holocene) and Japanese archipelago (Pleistocene) in the east, southern China and northern Vietnam in the south. Water deer also inhabited Taiwan historically, however this population presumably became extinct as late as the early 19th century.
Water deer are indigenous to the lower reaches of the Yangtze River, coastal Jiangsu province (Yancheng Coastal Wetlands), and islands of Zhejiang of east-central China, and in Korea, where the demilitarized zone has provided a protected habitat for a large number. The Korean water deer (Hydropotes inermis argyropus) is one of the two subspecies of water deer. While the population of Chinese subspecies is critically endangered in China, the Korean subspecies are known to number 700,000 throughout South Korea. In China, water deer are found in Zhoushan Islands in the Zhejiang (600–800), Jiangsu (500–1,000), Hubei, Henan, Anhui (500), Guangdong, Fujian, Poyang Lake in Jiangxi (1,000), Shanghai, and Guangxi. They are now extinct in southern and western China. Since 2006, water deer have been reintroduced in Shanghai, with a population increase from 21 individuals in 2007 to 227–299 individuals in 2013. In Korea, water deer are found nationwide and are known as gorani (고라니).
Water deer inhabit the land alongside rivers, where they are protected from sight by the tall reeds and rushes. They are also seen on mountains, swamps, grasslands, and even open cultivated fields. Water deer are proficient swimmers, and can swim several miles to reach remote river islands. An introduced population of Chinese water deer exists in the United Kingdom and another was extirpated from France.

### South Korea

Despite a listing of "vulnerable" by the International Union for Conservation of Nature (IUCN) in South Korea, the animal is thriving because of the extinction of natural predators, such as Korean tigers and leopards. Since 1994, Korean water deer have been designated as "harmful wildlife", a term given by the Ministry of Environment to wild creatures that can cause harm to humans or their property. Currently, certain local governments offer bounties from 30,000 won ($30) to 50,000 won ($50) during the farming season. However, the hunting of water deer is not restricted to the warm season, as 18 hunting grounds were currently in operation in the winter of 2018.
| | 1971 | 1990 | 1999 | 2005 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 |
| Density per 100 ha (1 km$^2$) of individuals | 0.4 | 3.7 | 5.3 | 6.2 | 6.6 | 7.3 | 7.5 | 6.9 | 8.2 | 7.8 | 8.0 | 8.3 |
| Deer kill (bounty hunting) | | | | | 11,269 | | 29,756 | 50,333 | 58,786 | 88,041 | 113,763 | |
| Deer kill (hunting) | | | | | | 1,500 | 13,904 | 3,943 | 10,944 | 14,982 | | |
| Deer kill (car accidents) | | | | | | | | | | | 60,000 | |

### Britain

Chinese water deer were first introduced into Great Britain in the 1870s. The animals were kept in the London Zoo until 1896, when the Duke of Bedford oversaw their transfer to Woburn Abbey, Bedfordshire. More of the animals were imported and added to the herd over the next three decades. In 1929 and 1930, 32 deer were transferred from Woburn to Whipsnade, also in Bedfordshire, and released into the park. The current population of Chinese water deer at Whipsnade is estimated to be more than 600, while the population at Woburn is probably more than 250.
The majority of the current population of Chinese water deer in Britain derives from escapees, with the remainder being descended from many deliberate releases. Most of these animals still reside close to Woburn Abbey. It appears that the deer's strong preference for a particular habitat – tall reed and grass areas in rich alluvial deltas - has restricted its potential to colonize further afield. The main area of distribution is from Woburn east into Cambridgeshire, Norfolk, Suffolk and North Essex, and south towards Whipsnade. There have been small colonies reported in other areas.
The British Deer Society coordinated a survey of wild deer in the United Kingdom between 2005 and 2007 and identified the Chinese water deer as "notably increasing its range" since the previous census in 2000.

### France

A small population existed in France originating from animals that had escaped an enclosure in 1960 in western France (Haute-Vienne, near Poitiers). The population was reinforced in 1965 and 1970 and the species has been protected since 1973. Despite efforts to locate the animals with the help of local hunters, there have been no sightings since 2000, and the population is assumed to be extinct.

### Russia

On April 1, 2019, a water deer was spotted using a photo trap in the "Land of the Leopard" national park in the Khasan district of Primorsky Krai, Russia, 4.5 km from the border with China. In 2022, the population of water deer in Primorsky Krai was about 170 individuals. Thus, the water deer became the newest, and 327th, mammal species to be listed among the fauna of Russia.

## Morphology
### Physical attributes

| Body length | Shoulder height | Tail length | Weight |
| 77.5–100 cm | 42–65 cm | 6–7.5 cm | 9–14 kg |
| 2.5–3.3 ft | 18–22 in | 2.4–3 in | 20–31 lbs |
The water deer has narrow pectoral and pelvic girdles, long legs, and a long neck. The powerful hind legs are longer than the front legs so that the haunches are carried higher than the shoulders. They run with rabbit-like jumps. In the groin of each leg is an inguinal gland used for scent marking; this deer is the only member of the Cervidae to possess such glands. The short tail is no more than 5–10 cm (2.0–3.9 in) in length and is almost invisible, except when it is held raised by the male during the rut. The ears are short and very rounded, and both sexes lack antlers.
The coat is an overall golden brown color and may be interspersed with black hairs, while the undersides are white. The strongly tapered face is reddish-brown or gray, and the chin and upper throat are cream-colored. The hair is longest on the flanks and rump. In the fall, the summer coat is gradually replaced by a thicker, coarse-haired winter coat that varies from light brown to grayish brown. Neither the head nor the tail poles are well differentiated as in gregarious deer; consequently, this deer's coat is little differentiated. Young are born dark brown with white stripes and spots along their upper torso.

### Teeth

The water deer have developed long canine teeth which protrude from the upper jaw like the canines of musk deer. The canines are fairly large in the bucks, ranging in length from 5.5 cm (2.2 in) on average to as long as 8 cm (3.1 in). Does, in comparison, have tiny canines that are an average of 0.5 cm (0.2 in) in length.
The teeth usually erupt in the autumn of the deer's first year at approximately 6–7 months of age. By early spring, the recently erupted tusks reach approximately 50% of their final length. As the tusks develop, the root remains open until the deer is about eighteen months to two years old. When fully grown, only about 60% of the tusk is visible below the gum.
These canines are held loosely in their sockets, with their movements controlled by facial muscles. The buck can draw them backwards out of the way when eating. In aggressive encounters, he thrusts his canines out and draws in his lower lip to pull his teeth closer together. He then presents an impressive two-pronged weapon to rival males. It is due to these teeth that this animal is often referred to as a "vampire deer".

## Genetic diversity

The mitochondrial DNA of samples from the native Chinese population and the introduced UK population was analysed to infer each population's genetic structure and genetic diversity. It was found that the UK population displays lower levels of genetic diversity, and that there is genetic differentiation between the native and introduced population. It was also found that the source population of the British deer is likely to be extinct. This has implications for the conservation of the different populations, especially as Hydropotes inermis is classified as Vulnerable in its native range according to the IUCN Red List.

## Behaviour

Apart from mating during the rutting season, water deer are solitary animals, and males are highly territorial. Each buck marks out his territory with urine and feces. Sometimes a small pit is dug and it is possible that in digging, the male releases scent from the interdigital glands on its feet. The male also scent-marks by holding a thin tree in his mouth behind the upper canines and rubbing his preorbital glands against it. Males may also bite off vegetation to delineate territorial boundaries.
Water deer use their tusks for territorial fights and are not related to carnivores. Confrontations between males begin with the animals walking slowly and stiffly towards each other, before turning to walk in parallel 10–20 m (33–66 ft) apart, to assess one another. At this point, one male may succeed in chasing off his rival, making clicking noises during the pursuit. However, if the conflict is not resolved at the early stage, the bucks will fight. Each would try to wound the other on the head, shoulders, or back, by stabbing or tearing with his upper canines. The fight is ended by the loser, who either lays his head and neck flat on the ground or turns tail and is chased out of the territory. Numerous long scars and torn ears seen on males indicate that fighting is frequent. The fights are seldom fatal but may leave the loser considerably debilitated. Tufts of hair are most commonly found on the ground in November and December, showing that encounters are heavily concentrated around the rut.
Females do not seem to be territorial outside the breeding season and can be seen in small groups, although individual deer do not appear to be associated; they will disperse separately at any sign of danger. Females show aggression towards each other immediately before and after the birth of their young and will chase other females from their birth territories.

### Communication

Water deer are capable of emitting several sounds. The main call is a bark, and this has more of a growling tone when compared with the sharper yap of a muntjac. The bark is used as an alarm, and water deer will bark repeatedly at people and each other for reasons unknown. If challenged during the rut, a buck will emit a clicking sound. It is uncertain how this unique sound is generated, although it is possibly by using its molar teeth. During the rut, a buck following a doe will make a weak whistle or squeak. The does emit a soft pheep to call to their fawns, whilst an injured deer will emit a screaming wail.

### Reproduction

| Gestation period | Young per birth | Sexual maturity | Life span |
| 170–210 days | 1–7 (commonly 2–5) | 7–8 months (does); 5–6 months (bucks) | 10–12 years |
During the annual rut in November and December, the male will seek out and follow females, giving soft squeaking contact calls and checking for signs of estrus by lowering his neck and rotating his head with ears flapping. Scent plays an important part in courtship, with both animals sniffing each other. Mating among water deer is polygynous, with most females being mated inside the buck's territory. After repeated mountings, copulation is brief.
Water deer have been known to produce up to seven young, but two to three is normal for this species, the most prolific of all deer. The doe often gives birth to her spotted young in the open, but they are quickly taken to concealing vegetation, where they will remain most of the time for up to a month. During these first few weeks, fawns come out to play. Once driven from the natal territory in late summer, young deer sometimes continue to associate with each other, later separating to begin their solitary existence. Young water deer are also known to grow faster and be more precocious in comparison to other similar species.