Initially, the long-haired winter coat is a pale, sandy brown colour, sometimes bordering on blonde, and often appears speckled with ochre owing to brown bands near the tip of the hairs. Towards the end of winter and into spring, the pelage of some populations can take on a slate grey hue, while others may present with a silvery appearance (see below). In summer they sport a darker russet/chestnut brown short haired coat stippled with black, the chestnut colour darkening along the upper back, redder on the head, and growing paler down the flanks. Several authors have noted that in Korea these deer exhibit a darker coat, more reddish on the head than those in China.
The area around the nose, eyes/eyebrow, along the chin and throat and the inside of the ears is off-white to buff. A darker stripe of fur extends around the top of the nose and terminates in dark grey or black labial spot on the lower jaw, just behind where the canine teeth protrude in males (see: Appearance - Doppelgänger deer?). This species lacks the distinct speculum (rump patch) present in other deer, although the rump may be slightly paler in the winter coat, and there is often a darker patch of coarse fur at the base of the neck that's most obvious in winter.
I'm not aware of any reports of fully melanistic (i.e., black) specimens, as are documented in other species (e.g. Fallow, Dama dama, and Roe, Capreolus capreolus), although I have seen photos and videos of Korean specimens with comparatively dark coats, particularly around the face. In Buckinghamshire, Sharon Scott has described to me some individuals with a very light coat, “almost white” in her words, but they have so far evaded our cameras. I know of only a single record of an albino animal shot in Sichuan province, south-west China, that Mr. T. Hance described in a short note to The Field in April 1888:
“I write to say that there is a specimen of an albino Chinese water deer (Hydropotes inermis) (Swinhoe), preserved in the Shanghai Museum. It was purchased in the local market in December, 1884, the sex a male, and is supposed to have come from the neighbourhood of Kading. The original colour of the eyes was almost brilliant red, and in size the animal does not differ from the ordinary specimens.”
I would be very interested to hear from anyone who knows if this specimen is still in the museum's collection or is aware of any other records of unusually colour pelage in this species.
Very young fawns are sparsely and indistinctly spotted with white. Spaced about four centimetres (1.5 in.) apart, the spots run in longitudinal lines from the base of the neck to the tail. Interestingly, the upper line of spots on the fawn's coat is more distinctive than the two lower ones, which are shorter and more irregular. According to Alfred Garrod, writing in 1877, this is a consequence of the spots in the lower two rows being formed not by white hairs, but hairs that are dark reddish in colour with a white tip not more than one-sixth of their length. In the adult's summer coat, by contrast, the hollow hairs are white for most of their length, the blackish-brown bands appearing in the upper one-third and ending with a light chestnut tip. The overall result is that the overlapping hairs give the general “ground colour”, while the blackish rings and chestnut apex provides the stippling that Robert Swinhoe commented upon in his original description in 1870.
The hairs on most of the head and body are coarse/stiff and long, 40-55 mm (1.7-2.2 in.), while those around the nose are very short, particularly in the summer coat. The fur covering the neck and face are shortest, with that on the neck and rump longest. Sporadic long whisker-like hairs are present on the face near the eyes, including the mystacial vibrissae that Pocock described in his 1923 paper to the Proceedings of the Zoological Society of London as being “tolerably numerous and of average length” on the muzzle, and five or six vibrissae around each eye. Additionally, there are several long quill-like hairs embedded in the chin and upper section of the throat; these are yellow in colour, owing to a pale or greyish at base with a subterminal ring of dark brown and a buffy tip.
Water deer fur is dense. Yeong-Seok Jo, John Bacus and John Koprowski, in their 2018 review of the mammals of Korea, give hair densities of 164 hairs per square centimetre (just over 1,000 per square inch) in July, increasing to nearly 400 per sq-cm (2,600 per sq-in.) by the autumn and peaking at 920 per sq-cm (5,980 per sq-in.) during the winter. In a chapter to the compendium Deer of China, published in 1993, Helin Sheng and colleagues presented the results of their anatomical study of guard hairs taken from the backs of several deer species. Those from water deer had a wavy appearance and averaged 48 mm (2 in.) in length, with an oval cross-section profile of 391 µm by 252 µm. (These are difficult values to picture, but if you were to lay them next to one another you'd fit about 26 in a centimetre or 67 in an inch, while stacked on top of each other 40 would be a centimetre and 100 would stand an inch tall.) The analysis also revealed that Hydropotes guard hairs lack a robust cortex, the tiny keratin fibres between the outer cuticle and inner medulla that gives the hair flexibility and tensile (stretching) strength. Instead, the medulla, the inner core that contains air spaces, makes up the full width and the cortex is degenerated.
What the findings of Sheng and her team suggest in practice, is that the hairs are light and very insulative, but they're fragile and prone to breakage because they lack the cortex that would normally afford elasticity and thus resistance. These observations tie in with mine and those of Arnold Cooke. Cooke has described deer taking on a “silvery” appearance late in the winter that seems to be the result of broken/damaged guard hairs, and I have been struck by how easily the hairs break when handled. Similarly, we know that water deer rapidly overheat when forced to run, while fawns are very susceptible to dehydration during hot summers. I have observed frost remaining on the back and rump of their winter coat for up to an hour after sunrise, and in their 2009 book Wild Deer in Britain, Roy Harris and Ken Duff note that when water deer lie on the snow, their weight makes an impression, but the snow does not melt. Taken together, these observations attest to the significant insulation provided by the fur.
The fragile nature of the hairs of the winter coat perhaps also goes some way to explain how it is shed so readily. Rutting water deer can lose large tufts of fur during fights and there is frequently a “puff” of fur observed when deer of either sex are shot. The propensity for fur to come loose varies with the age of the coat, with Derbyshire-based taxidermist Matt Hargreaves telling me that you can virtually blow the fur out of the coat in February/March, while the pelage is far more durable between October and December. Similar observations were reported by Paul Childerley and I have found the early December coat to withstand moderate tugging before the fur comes loose. My annecdotal observations of the hair roots of winter fur suggest a small bulb (root), which seems to desiccate and shrink as the season wears on and the moult approaches. This root is narrower than the width of the hair shaft that's attached to it and connected to the shaft via a thin and fragile junction. Looking at tufts of fur lost during probable chases, many are broken at this junction.
Writing in 1950, Kenneth Whitehead suggests that the high density of hairs and that they come away so easily may be an adaptation to absorbing the force of a canine strike during the rut. Matt Hargreaves alluded to the same explanation, describing winter water deer as being ‘built like pillows' to protect their comparatively thin skin. Given that both bucks and does have equivalent pelage, however, I wonder whether there might be an additional evolutionary driver. Water deer evolved in the presence of large feline predators (recently leopards and tigers, but prehistorically, the Asian scimitar cat Homotherium ultimum, the early lion Panthera youngi and probably the giant cheetah Acinonyx pardinensis), which tend towards a launch-and-grab style attack on the rump of prey. Perhaps the propensity of the winter coat - sported when vegetation is lowest and therefore cover is at a minimum - to come away makes it difficult to gain purchase on a fleeing deer and may facilitate escape.
By contrast to the winter coat, Paul Childerley tells me that the summer pelage is essentially the same as that of a Roe deer (Capreolus capreolus) and is much less prone to fur loss.
Water deer undergo two moults, transitioning between their short, reddish summer coat and longer buff/speckled winter pelage. Broadly speaking, the first moult happens during the spring and the second in the autumn, but the exact timing varies considerably and appears to be influenced by local conditions, particularly the weather and/or temperature. Indeed, I have seen red-coated animals at Whipsnade during December and, in their 1981 report on the ecology of water deer at Woodwalton Fen, Arnold Cooke and Lynne Farrell noted the presence of such individuals even in mid-winter. They also observed the moult to be about a month later in 1978 than in 1977. At Whipsnade, I observed several animals moulting from their winter coat in mid-June 2019, following a cold and wet spring.
The spring moult into the summer coat typically takes place during April and May, resulting in a tatty/scruffy appearance; the coat covered in loose hairs with some tufts missing. At Woodwalton Fen, Cooke and Farrell categorised “poor moult” coats into two types: those with tufts of loose hair hanging out or missing, and rough or bald patches, particularly around the back and neck; and those that looked like they had large clipped/shaved patches, often typically on the back, where the hair had broken about two-thirds of the way down the shaft from the tip, giving a silvery/glinting appearance to their backs. Between 1976 and 1979, they recorded 17% of the 135 deer they observed with poor coats moulting in March, 53% in April and 17% in May.
Fawns moult out of their “hider pelage” during the summer, their coat having lost its spots and taken on a woolly/shaggy appearance by the end of August. Moulting back into the winter coat is, in my experience, a less obvious process, beginning during late-summer and early autumn, and with most having completed by November.