Water Deer Territoriality - Scent Marking

We humans tend to resort to passive means of proclaiming territory ownership, “keep out” signs and fences, which are followed with more direct action if warnings aren't heeded. Water deer apply a similar dual-level approach, with scent being applied to the environment in lieu of plaques and physical barriers. Scent, of course, is transient and must be reapplied regularly to sustain the message, so substantial time and effort goes into scent marking and patrolling territories during the rut. Anywhere in a territory can be marked, but most are concentrated along the boundaries. In China, at Poyang Lake National Nature Reserve, for example, Lixing Sun, Bing Xiao and Nianhua Dai identified 366 marking sites, the majority of which (67%) were found near territory borders; 114 (31%) were on the inner areas of territories, and only seven (2%) on territory-free areas.

Interestingly, however, Stefan Stadler noted that, at Whipsnade, scent marking was not obviously a deterrent for other males, and intruding bucks were never observed to shy away having just sniffed a scent mark left by the territory owner. Hence, it may be that marking serves to reassure the territory holder of their status. Indeed, Francois Feer observed the dominant buck in his study group superimposing the marks left by the subordinate animal, and in Deer, Raymond Chaplin described how territorial scrapes are reinforced after challenges:

“A scrape is a small area of ground stripped of grass ... to which the territorial male returns time and time again to mark. Scrapes are situated around the periphery of the territories and are visited by contenders before advancing on the dominant male. After sniffing the scrape the contender rubs his face two or three times in it and briefly squats over it. When the contender has been displaced the holder returns to the scrape, paws with his forefeet, rubs his face in it, squats over it and then returns to the centre of his area.”

The frequency and intensity of scent marking is greatest in early winter, although Stadler observed males scent marking on and off throughout the year, implying some loose territory may be retained year-round. I've personally observed very little scent marking outside of the winter and early spring, although I have trailcam footage of bucks seemingly patrolling, with tail held up, one in mid-July 2022 and one in early July 2023, and watched a buck undertake “excretive marking” (see below) while feeding during June 2021. Similarly, at Poyang Lake during 1988/89, Lixing Sun and Bing Xiao found that marking behaviour and chases between males declined from four per hour during the winter to once every two hours in April. In other words, bucks scent marked eight times more often during the winter than by mid-spring, indicating a significant drop in territorial behaviour outside the rut. Also in China, at Huaxia Park, observations on six bucks by Xiao-Jun Yu and his team spent significantly more time undertaking rutting behaviour, including scent marking between October and January than at other times of the year - correspondingly, testosterone levels were at least twice as high during the rutting period than outside it. Interestingly, though, there was no significant difference in forehead marking between rut and non-rut periods.

While data are lacking, the age of the buck and the presence of other males and/or a concentration of females in the area likely also dictates the intensity and duration of scent marking. Certainly, Feer found that removal of a dominant buck from the enclosure significantly reduced scent marking by the subordinate, and scent over-marking of the dominant animal was substantially less outside of the rut.

Broadly speaking, the scent marking behaviour of Chinese water deer can be grouped into two categories according to the glands being employed, the action used to apply it, or the subject being marked: ground and vegetation marking, the latter consistently including the use of the forehead, suborbital/preorbital gland and mouth/tusks.

Ground marking

This approach utilises metabolic waste products (i.e., urine and faeces) to mark areas within a territory and often to over-mark excretions of females or other bucks. This can be differentiated from simple urination or defaecation by the stereotyped behaviour accompanying it and the presence of only a small quantity of waste. Typically, when simply voiding waste, a deer will deposit a substantial pile of pellets or stream of urine, so the controlled manner of deposition here implies a function more significant than simple waste removal. Indeed, in his Deer of the World, published in 1998, Valerius Geist described how, when faeces play a significant part in social life as a marking agent, as seems the case in water deer, the defaecation posture tends to be exaggerated. In other species, pellets are dropped haphazardly, and the posture is close to normal stance. Urine invariably carries volatile metabolic compounds that other water deer can interpret, and the eminent British zoologist Reginald Pocock described, in 1923, a “thickened glandular rim” surrounding the anal orifice in this species, which may be responsible for depositing scent on to faecal pellets.

Ground marking almost invariably begins with the buck scraping the ground two or three times with one front leg, usually followed by one or two scrapes with the other, before taking a couple of steps forward, assuming a hunched stance and depositing a few drops of urine or a few pellets (sometimes both) into the rucked-up area. In his description of the behaviour of five animals kept at Wuppertal Zoo in Germany during 1980, Feer noted that when bucks scratched the ground with forelegs it was combined with defecation and urination in 24% and 35% cases, respectively, and both together in 12%. The dominant buck was recorded pawing the ground and urinating into the scrape more frequently than the subordinate. This marking behaviour was never observed in females, and my experience has been that females only tend to scrape the ground before lying down. Likewise, at Poyang Lake, Sun, Xiao and Dai never observed urine/faecal marking in females, and noted how, despite being common during the rut, it was seen only once in a buck outside of the breeding season. The scraped area, which is typically less than 30 cm (12 in.) square, may also be marked with the forehead/preorbital glands, either in combination with or in lieu of urine/faeces.

The pawing presumably serves a dual purpose, clearing the ground of debris/vegetation for the deposition of urine/droppings, and creating a rucked-up area that is visible to other passing deer. There may also be scent deposition during the scraping, although if the intention is to deliver scent through the scraping it's curious that only the front feet are involved, as they have significantly smaller glands than the hind feet (see: Scent glands).

Use of urine and faeces is the most frequently observed method of scent marking and during the rut bucks can often be seen stopping periodically to scrape the ground and squat over it. This may be done several times in very close succession during parallel walks. At Whipsnade, Stadler recorded that it was twice as common in adult males as yearlings, and that territorial bucks marked more often than non-territory-holding males. Stadler also observed that marking would frequently happen on an area previously defecated or urinated on by another deer of either sex, and bucks sometimes performed the marking during sexual encounters with does, having completed a flehmen response after sniffing their urine. Arnold Cooke has documented small piles of pellets littering territory boundaries in Cambridgeshire and, in Muntjac and Water Deer, he notes that “territorial bucks often have stuck-out tails because of their regular marking with dung”, which I have also observed.

On the rides at Woodwalton Fen, Cooke and Lynne Farrell recorded reduced pellet group size (i.e., fewer pellets per group) but an increase in the number of groups as the rut progressed, from a low in autumn to a high in winter and reaching a peak in January. Bucks decrease their feeding during this time, and need to ration faeces to allow more strategic deployment. Similarly, Lixing Sun, Bing Xaio and Nianhua Dai, studying deer at Poyang Lake National Nature Reserve in Jiangxi, found that during the rut, bucks appeared to produce more, smaller pellets that were much more likely to be left in groups than outside the breeding season. On average nine or ten pellets per cluster were left during the rut, while does fairly consistently produced an average of 73 pellets per defaecation throughout the study; outside the rut, bucks averaged 67 pellets. Bucks also urinated only a few drops at a time during the rut. This sparing use of faeces and urine increased the number of places a buck could mark.

Sun and his co-workers found that urine was always present at marking sites, and was accompanied by faeces and/or pawing much (i.e., 84%) of the time. In their 1994 paper to Acta Theriologica, the researchers suggest that urine may be the “cheapest” marking material, while also moistening dry ground to help with scent propagation. Interestingly, while watching the water deer at Whipsnade during the late 1960s, Raymond Chaplin noted how, despite careful attention on many occasions, no visible amount of urine or faeces was voided into scrapes.

It should be noted that while faeces marking was significantly more common during the winter, Stadler recorded it at Whipsnade during the summer months, too. In his thesis, he described how bucks didn't interrupt their feeding to mark, or paw the ground beforehand, but the presence of only a few pellets or droplets of urine implied a behaviour that continued to function as more than waste removal.

Vegetation marking

This is perhaps a somewhat clumsy aggregation of scent marking behaviours that might represent three separate types: forehead marking, preorbital marking, and vegetation wounding with the teeth. Unfortunately, it is extremely difficult to get a clear enough view of the activity in sufficient situations to be confident that they don't all share the same goal of applying suborbital scent to vegetation, and hence they are considered together pending further data.

Head marking takes the form of a male deer, having assumed a tense body posture, rubbing front areas of its face against the ground and objects such as low branches, pieces of wood, fences, the stems of thin vegetation et cetera. In the literature, there are various descriptions of deer at Whipsnade, Wuppertal Zoological Park in Germany and Poyang Lake in China marking ground vegetation by gently rubbing their foreheads and/or preorbitals up to 15 times against twigs, plant stalks, tufts of grass and pieces of wood in bouts of three or four vertical head movements. At Whipsnade, I have seen bucks marking tall grasses, sedges and nettles, as well as short grass/turf, and in one instance at Woburn a buck forehead marked a wooden fence. Similarly, Arnold Cooke, in Muntjac and Water Deer, mentions one potential trailcam clip of vegetation marking “that appears to show a thin sallow stem being brushed by the preorbital gland as the forehead rubs against it” at WWF in late December 2018, and Xiao-Jun Yu and his team observed their six captive bucks at Huaxia Park in Shanghai rubbing their lachrymal (i.e., preorbital or infraorbital) glands on fences in their enclosure. The aim of this rubbing behaviour appears to be the transfer of scent from the preorbital gland to the object in question.

On several occasions I've observed bucks periodically wiping their forehead on short grass, during which the front of the face makes square contact with the ground, while patrolling their territory. Arnold Cooke suggested to me via e-mail that ground marking may reflect the habitat:

“I do wonder whether it might be site specific - where they haven't got taller vegetation, they anoint the ground. But I'd have expected ground-anointing at WWF in open areas where they lek (and where I've had the cameras).”

It's possible that flush contact of the face with the ground allows both preorbital glands to be applied simultaneously, and/or the application of preorbital and forehead scent, although anatomical studies have failed to identify any specific glands in the skin on the forehead, as are well known in muntjac. Nonetheless, Norma Chapman has pointed out that water deer may possess hither-to undescribed enlarged sweat or sebaceous glands in the skin of the forehead. Such glands are found in roe deer as well as black- and white-tailed bucks, and appear to be an important source of scent during the rut (see Scent glands), although Aleksey Danilkin's observations suggest that the enlargement of these glands in roe corresponds with a significant thickening of the skin on the forehead that has not, to my knowledge, been described in water deer. I would be interested to hear from any stalkers who have observed such a change in skin thickness during the winter. (Note: Francois Feer reported that females may engage in head-rubbing, particularly rubbing of the ears and posterior parts of the head, but considered it a comforting activity rather than scent-marking behaviour of bucks owing to the lack of precision.)

Vegetation marking behaviour can be prolonged and frenetic. One buck I observed at Woburn on 10^th December 2022, for example, spent just under three minutes rubbing its head against the same clump of grass before moving on, while Stadler watched a yearling territorial male rubbing its forehead for six minutes without interruption at Whipsnade in December 1988. At Poyang Lake, Lixing Sun and colleagues recorded bouts of forehead marking that lasted between five seconds and four minutes, the bucks sometimes scraping the ground and mouthing the vegetation. Centre d'Écologie générale de Brunoy naturalist Francois Feer, for example, described his dominant male as rubbing his forehead against a branch or small vertical trunk at the height of the withers up to six times in a single bout, sometimes repeated after a second sniff. In his 1982 paper, Feer wrote of how the dominant buck “marks a lot with the forehead”. Animals kept in Raymond Chaplin's garden at Needingworth in Cambridgeshire also appeared engrossed during head rubbing - the same object was marked several times per day, across many days during the rut.

It's interesting to me that water deer should require spending such a protracted period so engrossed in preorbital marking. Does this perhaps represent a relatively weak secretion, a reduced secretion (the glands are certainly smaller than those of, for example, muntjac), the bucks becoming transfixed or some other factor, or combination of factors?

As noted by Roy Harris and Ken Duff in Wild Deer in Britain, the tusk on the corresponding side of the face being rubbed may sometimes be employed to hook the stem and ensure contact with the preorbital gland. At West Midlands Safari Park, Robert Lawrence reported bucks holding saplings up to 13 mm (0.5 inch) in diameter between the tusk and the mouth and rubbing their head up and down energetically, sometimes for several minutes. Lawrence observed that this rubbing left the stem extremely smooth at a height of about 15 to 40 cm (6-15 inches) from the ground; very occasionally, in the case of one wild cherry sapling, the bark was found to have been broken. Sun and his team observed something similar, with Chinese mugwort (Artemisia selengensis) stems exhibiting marked sections 10 to 20 cm (4-8 inches) in length between five and 45 cm (2-18 inches) above the ground. In only one case, however, was scent transfer apparent, a buck using his right preorbital gland to mark a mugwort stem. The consensus I get from the literature is that, given how the tusk is not always employed and can only have a limited application, most authors consider the slight abrasion sometimes caused by the rubbing to be collateral damage from the preorbital scent deposition.

Finally, the teeth may be engaged more intensively during marking than just as an aid to positioning. The buck that I observed engrossed in preorbital/forehead marking for several minutes in 2021 also periodically licked and nibbled at the clump of grass between bouts of marking. I witnessed a similar mouthing of grass by a buck at Whipsnade in December 2018 that followed a flehmen response to a patch where a female had been laying. Likewise, Feer described how, on rare occasions (i.e., 5% of markings), the buck's forehead rubbing was accompanied by alternate scraping of the trunk with the incisors, and Stadler documented “nibbling” of vegetation by bucks also showing forehead marking at Whipsnade. Additionally, Stadler described a specific “tooth marking” behaviour from one buck. A long grass stalk was taken between the jaws and the animal moved its head side to side six to eight times, keeping the stem between the molars, resulting in the upper layer of tissue being scraped off the frond. The buck sniffed and nibbled at the stalk intermittently, suggesting to Stadler that tooth marking may be an extension of the nibbling at objects. I know of no other descriptions of this behaviour.

In their 1994 paper to Acta Theriologica, Sun and his coworkers suggest the intention of tooth marking is to create a wound. The authors consider that wounding plant bark may have several roles: trapping some odorous compounds in the sap after it dries, thereby allowing a slow release over time; it may create a moist substrate to facilitate propagation of chemical signals; and that it is typically done at head height may make it an obvious visual signal to other deer.