Observations at the Poyang Lake NNR in Jiangxi adequately reflect the breeding associations described in the literature for both England and France, and with my observations. Between October 1988 and January 1989, Lixing Sun and Nianbua Dai noted that males showed propinquity with females up to three days before copulation, and little association afterwards. While a couple of bucks associated with only one doe, most were seen with two or more, suggesting the mating system was polygynous. Water deer do not appear to be polyandrous, however, and while each buck copulated with, on average, 1.75 females, does were only observed copulating with a single buck. Repeated copulations by the same pair were observed on several occasions.
The close association in the run-up to mating described by Sun and Dai is a common trait observed in mammals and appears to be a response to females being receptive (i.e., “in heat”) for only a short period. In other words, the oestrus phase of a female's oestrous cycle is short, and males don't appear able to accurately calculate when it will begin, hence they closely follow them to ensure they don't miss their window of opportunity. Indeed, in their 1995 paper to Mammalia, Sun and Dai note how does appear to be receptive for only about 24 hours, based on a captive female that appears to have been observed by Fei Yan Ma, presumably at Huxia Park.
A faecal hormone study at Branféré Zoological Park, carried out by a team from the Muséum National d'Histoire Naturelle led by Robert Mauget, suggested, however, that females were only receptive for a few hours per oestrous cycle. Mauget and his co-workers found the peak of “association behaviours” of bucks to does corresponded with the periods when the females had the highest levels of faecal hormones. The researchers propose, in a 2007 paper to Mammalian Biology, this may be a strategy prone to failure in low density populations as bucks must monitor each doe within their territory closely. Alternatively, this may explain why bucks set up small areas where does feed—they could perhaps take their cues from other males as to when does come into season. Raymond Chaplin's observations suggest a doe will re-cycle if she's not mated. One of his captive females showed oestrous behaviour on 20th/21st December and again on 3rd/4th January, the latter time being mated.
The art of woo
During his time at Whipsnade, Stefan Stadler classified 12 different sexual behaviours, subdivided into courtship and mating. Courtship behaviour was commonly seen, but mating was seldom witnessed. Indeed, over the course of 55 hours spent in the field spanning three rutting periods (1986-1989), only 18 “matings proper” were observed. Within the bracket of courtship, Stadler described five behaviours.
Males approached females in a slow walk or trot, depending on their degree of sexual motivation, with their necks stretched low (below horizontal). As they neared the female the head was rotated continuously, resulting in an ear-slapping, and often whistled (squeaked). Unreceptive females typically jumped up and trotted a short distance away, at which point the male would either follow her in the same manner for a short distance or move to another activity - the buck may scent mark before returning to grazing/resting. Stadler named this the tending approach, while in his unpublished research notes Chaplin referred to this as “wuffling” after the snorting noise the buck makes, and it is one commonly observed during the rut. In a similar vein, an unreceptive female may remain lying for a short period while the buck sniffs and/or nuzzles her, before getting up and moving away; sometimes the doe will also ear-slap before going. This second behaviour is what Stadler called the tending gait. The male-lying-down activity involved a buck lying down directly in front of the doe while ear-slapping. Again, unreceptive females would get up and move as soon as their tail was sniffed, and the buck would subsequently sniff where she had been lying.
It has largely been my experience, too, that does are more likely to stand their ground when approached by a buck if close to or in oestrus, sometimes touching noses, while unreceptive females typically run away from amorous bucks who disturb their grazing or rest. Arnold Cooke and Lynne Farrell have similarly described this behaviour. Sharon Scott's observations suggest, however, that does occasionally fight back if they're disturbed on a particularly good feeding area.
During the winter 2018 rut, Sharon described watching a buck chasing a doe, the doe spinning around and rearing up on her hind legs to “box at the male” akin to hares. I have only observed something similar once, at a site near Woburn in December 2019: a buck approached a doe, his head down and ears slapping, and the doe danced around the buck, rearing up briefly to what I can only describe as “scissor kick” at him with her front feet. Stadler talks about does fighting with one another, including rearing up like this, but makes no mention of them doing it towards males, and Arnold Cooke tells me he has never seen a female turn on a buck. In two instances, prior to getting up and retreating, I have observed females mirror a buck's ear-slapping in a manner that suggested irritation/annoyance at having been disturbed. If the female doesn't yield, the buck may vocalise, and the following is an excerpt from my notes of behaviour observed Whipsnade on 14th December 2017:
“A buck rushed at a resting doe, stopping short in front of her when she didn't move and slapping his ears. He then strutted around, scraping the ground with his front feet and making a chirruping/chittering noise, almost as if frustrated.”
I have also known bucks to chirrup and squeak while pursuing a doe.
When males sniff either the doe or the couch in which she had been resting, they frequently engaged in flehmen behaviour, involving stretching their head and neck vertically and pulling back the top lip slightly, resulting in a grimace-like expression. When East German zoologist and Leipzig Zoo director Karl Max Schneider first coined the word “flehmen” in a description of the behaviour in 1930, the term translating from German to mean “baring the front teeth” or “looking spiteful”, he speculated that it might be an expressive behaviour, but we now know it's a means of passing a sample across a specialised chemoreceptor for hormone assessment. The vomeronasal organ (VNO), sometimes also referred to as the Jacobson's organ after the Danish surgeon who wrote about it in 1813, is a small diamond-shaped bulb of tissue forming part of the nasopalatine duct that runs along the roof of the mouth. It is theorised that the act of flehmen serves to move fluid-based pheromones (i.e., in the urine or vaginal secretions) from the mouth to the VNO for analysis, allowing the male to assess the reproductive state of the female.
Stadler observed flehmen 59 times during his study, 57 (97%) of which were by males and the remaining two (3%) by females, with flehmen frequencies the same between adult and yearling bucks. As we might expect, the bulk of flehmen occurred during the rut, being recorded only once in the summer. Gérard Dubost and his team at Branféré also observed bucks flehmen (I could find no reference in their papers to does exhibiting the behaviour), noting that males made between one and three “flehmen gestures” per bout, each lasting two to five seconds. Arnold Cooke noted in Muntjac and Water Deer that bucks periodically check the reproductive status of does by flehmen, and I have observed the behaviour a handful of times in bucks both at Whipsnade and on Bedfordshire farmland, although I see it less frequently in this species than, for example, red or fallow. In my experience, it is also more muted than in other species, with the top lip barely retracted. Indeed, I have several trailcam videos that show the head lifting and neck stretching that often accompanies flehmen, but without any obvious pulling back of the top lip. Curiously, Francois Feer didn't document the behaviour during his study.
In his unpublished research notes, Chaplin described repeated and periodic checking of the doe by the buck:
“From dawn to dusk the male investigates the female at approximately ten to twenty minute intervals. Judging from the noise, this also continues at night.”
Chaplin goes on to note that about 36 hours before oestrous the doe doesn't flee from the buck, who will lick her head, rump and anus while she also nuzzles him. Around two hours before she's receptive, the female “becomes very fidgety” and the male is particularly attentive.
The final courtship behaviour Stadler described was herding. Some males actively herded females, trying to keep them within the boundaries of their territory, and this occurred mostly during December. At times herding behaviour appeared quite sophisticated, involving the buck circling one or more females at between five and 20 metres (16-66 ft.) in a bid to keep them within the centre of his territory. Stadler noted that bucks were often observed standing motionless with one foreleg lifted for five to 20 seconds during herding. Males successfully herded females in 14 (70%) of the observations, although in two cases of human disturbance the bucks were unable to encourage the does back, despite following them out of his territory.
At Branféré, Dubost's team classified sexual interactions by males into three groups. The approach, during which they advanced on the female with neck stretched and nose close to the ground, often emitting soft “groaning calls”. The buck would sniff the doe's rear or the spot she'd been lying in before flehmen. If the female remained lying as he approached, the buck would ear-slap and sometimes gently kick her with his foreleg to prompt her to stand up. Second was the pursuit, which tended to be a buck following a doe at walking pace, occasionally sniffing at her genitals. The researchers never observed a buck to lick a female's genitals, although Francois Feer recorded this twice, and I have observed it twice among free-range captive animals. Finally, there was the mount.