Water Deer Behaviour - Social Behaviour

It is not uncommon to see substantial numbers of water deer aggregating, and even in his early observations on the species, Robert Swinhoe mentioned to Glover Allen an instance when what Glover recited, in his 1940 The Mammals of China and Mongolia, as “a herd of twenty was put up in the great marsh beyond the Hangchow Bay sea-wall, near Fenghsien” about 20 miles south of Shanghai. Here in the UK, larger groupings tend to be more commonly reported in open habitats, particularly during the late winter and early spring as the days warm and plant growth resumes. Indeed, Arnold Cooke observed one, in his words, “remarkable aggregation” of 16 deer grazing on a recently mown mixed fen area of about a hectare inside the nature reserve at Woodwalton Fen on 14th February 2011 at 16:30. Similarly, during his Whipsnade studies, Stadler found the largest group to contain 15 animals. During an early afternoon in December 2022, I counted 35 in a single field on an estate in Bedfordshire, and the largest aggregation I'm aware of occurred in October 2019, when Stephen Plummer counted 112 deer in a single field on the same estate, although it should be noted that this population is managed for stalking and the deer live at very high density.

It is important to recognise, however, that such assemblages appear to mostly be associations of convenience, the animals utilising good feeding and/or resting areas simultaneously, and water deer show no tendency towards the herding behaviour we see in red (Cervus elaphus) or fallow deer (Dama dama). This is noticeable when an aggregation is disturbed; deer scatter in all directions rather than fleeing together as a cohesive unit (herd). Equally, there is no apparent tendency for one deer to approach another just because it has seen it, unlike in herding species. Nor is one water deer particularly likely to pay more than a cursory interest to the barking or fleeing of another, and I have seen footage of one watching from a treeline no more than four metres (10 ft.) away as a buck in the open was shot, making no attempt to flee until the stalkers approached to retrieve the carcass. In a second case, a buck remained lying in the grass only a couple of metres from a doe which was shot. Indeed, there is very little indication of any sustained social cohesion in the species.

Lixing Sun observed that water deer at Poyang Lake NNR in Jiangxi, China tended to form larger groups during the breeding season (particularly early on, in November) and were most likely to be solitary during parturition (May-July). In a 2002 paper to Acta Zoologica Sinica, Sun explained:

“The reason why the group size fell into the lowest point in the parturition season was that each female actively sought a quiet location to give birth and care for her fawns. Males that used to be grouped with all-female groups became solitary, too. As fawns grew and could follow their mothers, females with fawns could group with other deer and consequently, the overall group size rose again.”

Sun also noted that the deer were more likely to form groups on short grass than when in tall vegetation, but the time spent feeding or engaged in vigilance behaviours didn't vary according to whether they were in a group or solitary, suggesting anti-predator response was not the reason for grouping. Stadler subsequently suggested that the seasonal and age-specific associations at Whipsnade may help with social development:

“In the autumn, female fawns associated increasingly with other female fawns and male fawns did increasingly with other male fawns. Thus, associating with like-sex individuals of the same age class may be actively sought by fawns and this may promote sex-specific behavioural development.”

Despite water deer sometimes forming large aggregations, most sightings are of solitary individuals or small groups of two or three animals, typically all females or, in my experience, a buck with one or two females. Out of 2,195 sightings logged at Woodwalton Fen between June 1976 and May 1979, for example, Arnold Cooke and Lynne Farrell note that 61% were of solitary deer. At Poyang Lake, Sun recorded that 90% of all groups were composed of only two or three individuals, and during the mating season, when bucks become aggressive towards one another and try to herd females, 70% of single deer for which sex could be attributed were bucks, compared with only 30% of females seen alone. Since January 2019, I've been camera-trapping on a farm in Buckinghamshire during the summer and winter, and of 647 trailcam videos of water deer collected up until February 2023, more than half show a solitary individual, and none recorded more than three deer travelling together. In captivity, Stefan Stadler sometimes encountered groups of seven or more during his Ph.D. studies at Whipsnade but, of nearly 17 thousand records of 175 individuals, 66% were of deer either singly or in pairs, and only 5% of all the groupings recorded consisted of five animals or more. My experience has been the same, and the largest group that appeared cohesive to me was composed of four individuals (a buck, an adult female with a young fawn and an adult individual of undetermined sex) at Ouse Fen in July 2024, which moved together into a patch of long grass and laid down, remaining there for the 15 minutes or so I was able to observe the area.

While the stable group formation we see in many other deer species doesn't appear to apply to Hydropotes, Cooke and Farrell have recorded a stable pair bond at Woodwalton, with a territory being occupied through the year by the same buck and doe. Likewise, in his 1982 article on the species, Bob Lawrence mentions that barren does may remain paired with a buck outside of the breeding season, and my experience has been that deer travelling or feeding in pairs outside of the main fawn-rearing period are usually either two does or a buck and a doe. I've also seen bucks accompanying does during the summer and have assumed the female did not have a fawn, until June 2024 when I observed a buck and doe together at Woburn. The doe returned to wash twin forms in the corner of the field and the buck followed, even briefly sniffing and licking one of the fawns that approached it, before sniffing and the doe's rear end and following her down the field, leaving the fawns to their own devices. I'm interested to hear from anyone who has seen a buck accompany a doe with fawns at foot.

At Branféré Zoological Park in France, Gérard Dubost and colleagues found no lasting bonds, even between mothers and their fawns; no notable interactions happened after the youngsters were more than about five months old. In their 2011 paper to Acta Theriologica, Dubost and his team wrote:

“There was no durable bond between mothers and own young. Four young born to focal females and still alive in the mating season had less contact with their mothers after the first period of the mating season than did unrelated young.”

There were also no special bonds apparent between the focal females and other mature individuals of the population, which tallies with the findings of Stadler at Whipsnade and Lixing Sun and Nianbua Dai at Poyang Lake. In his thesis, Stadler notes that although females sought other females outside the fawning period, the associations were temporary, and no long-lasting associations were observed between does at Whipsnade. There are, nonetheless, a few reports of what appear to be congenial interactions between adults, most notably does.

During his thesis on muntjac and water deer behaviour, completed in 1971, Wolf-Peter Scherpe observed “soziale körperpflege” (social grooming) between does. Francois Feer, writing in 1982, described six instances of “léchage mutual” (mutual licking) between females, the two animals licking one another on the forehead, around the eye, on back of the ears and on the neck. The females also rubbed their foreheads against each other's neck, and Feer considered this was probably a mother-daughter pair. Feer also noted that his dominant buck had most frequent contact with one female in particular and suggested that such associations could represent rudimentary coupling. Similarly, Raymond Chaplin's video of the water deer kept in his garden during the late 1960s and early 70s shows one of the mature bucks (“Max”) lying very close to an adult doe (“Pippa”) while chewing cud, and even Pippa licking both his preorbital glands. Chaplin told me that these two were virtually inseparable, spending a great deal of time “nuzzling” one another, and always laid together at night while chewing cud.

In his thesis, Stadler suggested that the confines of captivity may force the manifestation of social behaviours that don't appear under more natural conditions. I have, nonetheless, observed grooming between fully grown free-range does at Whipsnade and Woburn on two occasions during the summer of 2022. The first instance, at Whipsnade, involved a group of three animals, a buck and two does, during which one doe licked at the hock of the other for several seconds, while the subject grazed. There was no obvious attempt to reciprocate. In the second case, at Woburn, an adult doe rose from her couch along a fence line where she was ruminating and cantered out to meet a second doe approaching from across the field. The deer briskly approached each other and engaged in a bout of mutual grooming that lasted about 40 seconds, at which point the first doe returned to her couch and resumed ruminating while the second moved further up the field. During the grooming, each doe licked the face, rear end, ears and flank of the other, and the second doe licked the right hock of the first. I presume that in both instances these two does were familial, possibly mother and daughter from the previous year (based on size difference), or siblings. I have seen a video from South Korea of well-grown water deer siblings grooming one another in the wild, specifically one licking the preorbital glands of the other, and have witnessed a young fawn licking the preorbital gland of its mother at Whipsnade in mid-June 2024 as well as twin fawns licking each others faces, ears and flanks, and also sniffing at each others rumps on several occasions.

At Branféré, Dubost and his team found licking to be very rare among water deer, and only recorded five bouts that were all a male licking the nose, body or rear of a female, but that the behaviour was never reciprocated. The researchers also documented contact between two deer being nose to nose sniffing (or nose to rump when bucks are assessing a doe's oestrous phase during the rut), and I have observed this on a few occasions both in captivity and in the wild. They observed that females touched noses with other females more often than they sniffed at their rears (178 vs. 68 encounters), while the opposite was true when males made contact with females (30 vs. 53 encounters). Females also touched noses with fawns on 214 occasions and sniffed their rears on 103, while fawns did both but slightly more nose touching than rear sniffing. Stadler reported social sniffing to be a common behaviour at Whipsnade, although most animals avoided one another for a period before close-contact sniffing could occur. Sniffing at the tail was more likely to result in withdrawal than sniffing at the head.

I'm aware of one report suggesting that adult females may associate even with young fawns in tow. On 25^th June 2023, Sharon Scott observed two does walking across a field in Buckinghamshire in parallel (i.e., a metre or so apart, apparently travelling together), each with a fawn following behind. Sharon wasn't sure whether the fawns were twins of one of the females (one looking older than the other) and the other doe was simply tagging along, or if each fawn was a singleton of the doe it was following. Additionally, I've often seen pairs of well grown fawns together without any obvious adult affiliation during the late summer and autumn, so siblings may remain in social contact after they sever ties with their mother. Age may also affect sociality, and in his Whipsnade thesis, Stadler described yearling males roaming widely between May and July, avoiding social interaction where possible, such that interaction rates dropped to zero, or near zero, during this period. Indeed, male fawns beyond about three months old were more likely to be found unaccompanied than females of the same age. Yearling females associated less with adult females during summer than winter, while they were likely to be found with adult males at a fairly continuous rate throughout the year. Overall, fawns and yearlings of both sexes were more likely to hang around in pairs or small groups than adults of either sex.

In terms of frequency of interaction between individuals, the only data I have are again provided by Stadler. Based on monitoring of 23 animals during daylight, each interacted with another about 2.6 times per hour, on average, such that any given deer interacted every 23 minutes or so. Males were seen to interact almost twice as often as females (i.e., every 18 minutes versus every 34 minutes), and nearly half of interactions (43%) happened during the rutting period; only 10% during the fawning period. When viewed seasonally, winter interactions were more frequent (every 22 minutes) than summer ones (every 39 minutes) and, among males, territory holders interacted with another individual once every six minutes during the rut, while non-territorial males did so only every 21 minutes. Purely in terms of interaction rates, males were the more socially active sex, albeit a substantial number of interactions were aggressive and coincided with the rut.

In summary, it appears that while Hydropotes inermis cannot be considered a social species in the same way as the larger cervids, they are not necessarily immutably antisocial, males during the peak of the rut and pregnant females around fawning perhaps being the exceptions. As a species, they appear broadly tolerant of other individuals in close proximity for much of the year, and in some circumstances, small, non-breeding related groups may form, particularly among related animals. While bonds may endure for some time, we do not know for how long nor how commonplace their formation is in the wild. In captivity, social bonds appear rare and reasonably short-lived, but Stadler proposed, in his 1991 thesis, that the mild inclination of females to tolerate like-sex individuals may be interpreted as a first step in the evolution of group living in female deer. Indeed, 'mildly sociable' seems like a fitting description of water deer, at least of females.