While females may cluster, males tend to be more territorial, seen either solitarily or accompanying one or more does. Water deer spatial arrangement is nonetheless flexible, and mature bucks may aggregate to feed, especially in the early part of the year when the rut is over and food is more limited or concentrated. Prior to this, however, as autumn draws to a close, the increase in circulating androgens results in tensions rising among mature bucks; they become increasingly aggressive towards one another, and many more territories (i.e., small areas actively defended from other males) are established. Stefan Stadler considered territorial bucks to be those that returned to the same small area shortly after being driven off by disturbance, which was generally not the case for non-territorial males or for females, and also showed scent-marking behaviour within the area.
Luck can play a hand, and Arnold Cooke has recorded a non-territory-holding buck mating on the territory of another at Woodwalton Fen in the winter of 2015/16, but during the rut it is typically only the territory-holding males that will breed. Indeed, males lacking a territory seem less attractive to does. Consequently, while not all bucks will maintain them year-round, the acquisition of a territory for the rutting season is important. Stefan Stadler, for example, observed 18 matings during his 27-month study at Whipsnade, 14 (78%) of which were by males known to be territory holders; in a further three (17%) the territorial status was unclear. Overall, territorial males accounted for 95% of the 419 bouts of sexual behaviour recorded during the study.
At Branféré Zoological Park in France, Gérard Dubost and colleagues reported that it was territory holders that courted does during the peak of the breeding season, while (limited) courtship from non-territorial bucks was only seen at the end of the season. During encounters between territorial and non-territorial bucks, territorial ones were usually victorious while non-territorial ones were usually defeated. Similarly, Francois Feer noted that his mature buck frequently displaced the subordinate one. During the rut, the dominant animal was found in areas where the females spent more than half their time on about 60% occasions, compared with only 9% of occasions for the subordinate. When the dominant buck was removed, the number of observations of the subordinate in the main female areas increased to just over 40%. In his garden, Raymond Chaplin also found that his mature buck “Max” was always dominant over the younger male, but the two lived peacefully until December, when Max relentlessly and aggressively pursued the younger male. According to Chaplin, threats continued through the fence once they were separated.
Studies at Branféré and Whipsnade confirm observations from the wild, which suggest that it's the females that control the distribution of males during the rut. At Poyang Lake National Nature Reserve in Jiangxi, China, Lixing Sun, Bing Xaio and Nianhua Dai found that the deer returned to the grassland around the lake to feed and breed, having spent the summer in the peripheral hilly areas. In their paper to Acta Theriologica in 1994, they note how females were displaced by human activity nearby and moved to the lake grasslands, spending the day resting on the beach before moving into the grassland in the late afternoon to feed and remaining there overnight. The bucks followed a couple of days later and set up small (0.5 hectare) territories in the grassland frequented by the females. The bucks remained on the territory while the females were there; a male left the area only if he failed to establish a territory, was ousted, or the doe he was associating with left his territory. Territorial stability was highest where female density was highest, suggesting bucks wanted to be where the most females were hanging out. Similarly, at Whipsnade, Stadler reported bucks defending areas with resources desirable to females, from which does could come and go unless they were in oestrous. When in season the buck would try and keep her on the territory by herding her:
“Territory holders did not defend a female (or a group of females), as females move freely over the ranges of several territory holders. When females were in or close to oestrus, and only at this time, males tried to keep those particular females within the boundaries of their territories by herding them. Thus, it seems more likely that males defended an area that contained resources valuable to the females. The mating system of the CWD population at Whipsnade Park may, therefore, be described as a resource defense mating system.”
In his unpublished research notes, Raymond Chaplin described a similar situation on Valley Meadow at Whipsnade during early December in the late 1960s:
“There were about 30 adult males on this field and 4 territories, each occupied by a dominant male (one of which was tagged) and one or two females. The females were resting in the centre of each territory. The territories, about 90 yards across, were actively contested. The animals present in this field and those that were contending as well as defending territories were all adult males. No male fawns were present. Other work on the farm necessitated movement round the area and fawns that were disturbed were very reluctant to cross the territories of adult males and were always chased off when they tried to do so.”
In their 1998 booklet, Arnold Cooke and Lynne Farrell concur with the aforementioned, explaining how males attempt to associate with females in their territory with increasing intensity as oestrous approaches. My observations in Bedfordshire and Norfolk are also in line with this: a male will closely associate with one or more females and chase away any other males that come within sight or scenting range. On several occasions I have watched a buck appearing to try and encircle the female to keep her in the area. Interestingly, as Stadler also described, if a buck fails to prevent a female leaving, he does not generally follow, instead returning to his own territory. This also aligns with Paul Childerley's experience at Beckerings Park of mature bucks refusing to leave their territories, even in the face of the cars and lamps of coursers, making them easy targets for the dogs. Perhaps such fidelity is wise; Stadler noted how territorial takeovers were witnessed at the park, and in several cases the deposed males failed to regain territorial status.
Territory boundaries are marked by a combination of vegetation fraying, scent application and small groups of strategically deposited droppings (sometimes only one or two pellets), the latter being found along the rides at Woodwalton Fen during the rut. See Territory and home range for further details, as well as a discussion on how territories are marked.