While it is difficult to generalise about the activity patterns of any species, deer in general tend to be crepuscular animals, meaning that they're most active around dawn and dusk. Water deer seem to broadly conform to this pattern, although it does vary according to the location, season, weather, and, I suspect, the individual.
While completing his Ph.D. at Whipsnade, Stefan Stadler observed that the year could be roughly divided into four, each representing periods of biological significance for the deer: winter (February to April inclusive) when rut was over and forage quality was poor; fawning (May to July) when the mother-offspring bond was most intense and vegetation cover and quality was highest; summer (August to October) when the mother-infant bond dissolved and vegetation height and some quality was reduced; and rut (November to January) with activity peaking in first half of December and vegetation height and quality much reduced.
Stadler observed the deer for six-hour periods and, based on 23 animals, established that most daytime activity was seen during the “fawning” period, accounting for around 210 minutes of the observation period. The “rut” period saw the second highest level of diurnal activity (200 mins), followed by “winter” (185 mins) and “summer” (160 mins).
The activity of water deer in the context of the rut is discussed in the Rutting and Courtship section.
Most studies, both here in the UK and in the water deer's native range, suggest they feed primarily around sunset and/or sunrise. In Huxia Park in Shanghai's Pudong New Area during the spring and summer of 2008, for example, Feiyan Ma found two main peaks in activity, one in the morning (06:00-07:00) and a second in the evening (18:00-19:00), with a much smaller third peak around midday (11:00-13:00). On the Stat Nature Reserve at Dafeng in eastern China during Feburary and March 2001, Xiaolong Zhang and Endi Zhang reported that water deer spent most of the daytime lying up among long grass in the wetland, well away from human disturbance, before moving into nearby wheat and rape fields at night to feed. From May 1988 to April '89, Lixing Sun and Bing Xiao studied the behaviour of 22 individually identifiable deer at Jiniushan Hill in China's Jiangxi province, and observed that daytime activity was divided up into two active periods during which the deer were on the move: sunrise to 10:00, and 15:30 to sunset. Between these periods, Sun and Xiao report in their 1995 paper to Zeitschrift für Säugetierkunde, the deer were mostly to be found resting, ruminating or sleeping. Unfortunately, the authors didn't breakdown their results by season, although they do note that most of the observations were between October 1988 and January 1989.
Hwa-Jin Lee and colleagues used remote camera traps to monitor mammal activity along the Baekdudaegan ridge conservation area in Korea between June 2015 and May 2016. They found water deer were the most commonly photographed mammal species (accounting for 20% of the photos), seen both during the day and night. Most camera trap photos (65%) were, however, taken overnight (i.e. 18:00-07:00), and the deer were frequently caught on the ridge around 19:00. Unfortunately, the data that Lee and his team provide, published in the Journal of Asia-Pacific Biodiversity during 2019, are difficult to interpret owing to scant information about the methods, lack of detail in the text and no separation by season. It appears, nonetheless, that water deer were relatively unaffected by hikers in the conservation area, being caught on the camera traps, on average, about 17 minutes after a hiker had passed by. (They don't give the range, but the standard deviation was 17:49, minutes and seconds I presume, which is slightly higher than the mean (17:01), suggesting substantial variation.)
The Baekdudaegan ridge findings are interesting because in Mammals of Korea, Yeong-Seok Jo, John Baccus and John Korprowski comment on how this species appears progressively nocturnal with increasing human disturbance. Arnold Cooke considered it likely that, given their “flighty” nature, water deer would probably become more nocturnal during protracted culling, while pointing out that data are lacking. Intriguingly, Paul Childerley told me that on ground he manages in Bedfordshire, if anything, the water deer are easier to cull at the end of the shooting season; the sunshine and spring warmth drawing them out into the open fields. They can certainly be rather skittish, though, and writing in his 1981 book Mammal Watching, Michael Clarke noted that they panic easily and need plenty of cover in which to hide, becoming more relaxed as cover increases during late spring and summer.
Clarke's comment ties in with my observations that, apart from bucks during the rut, water deer tend to flee at even relatively mild disturbance, and it's not uncommon for one to explode out of a ditch or field margin that would've gone completely unnoticed had they stayed put. That said, Bedfordshire-based naturalist Stephen Plummer recently observed a reasonably unfazed doe at one of the counties country parks, which continued to graze unperturbed within about 100m (328 ft.) of him and his wife in February 2022.
In the UK, Clarke described how water deer feed primarily at dawn and dusk, with shorter midday and midnight bouts. Endi Zhang, during his Ph.D. studies at Whipsnade Zoo, found peaks in feeding between 06:00 and 10:00 and again between 17:00 and 21:00, but didn't provide any details more than to say this was during spring and summer, and that there was a lull between 11:00 and 13:00. Zhang's findings correspond with my own observations at the zoo, where outside of the rut most of the deer are resting during the day, although I have noticed a tendency for some to be found grazing briefly during the early afternoon. During the rut, both sexes can be found active throughout the day.
In Muntjac and Water Deer, Arnold Cooke reminisces about how the start of the decades-long study that he and Lynne Farrell conducted in and around Woodwalton Fen in Cambridgeshire began with three years of trying to get a handle on the movements and activity patterns of the deer on the reserve. Through their repeated and meticulous surveys, they found that the deer's activity was closely associated with sunset, and almost four times as many sightings were recorded in the half an hour leading up to sunset as in any of the other 30-minute periods in the two hours leading up to it. This relationship was consistent throughout the year, and while there was a tendency to see more deer during the daytime in winter, overall, only about 10% activity took place during between sunrise and sunset.
Deployment of remote cameras on the reserve allowed Cooke an insight into how water deer activity varied with habitat and season. Between November and February in areas of sallow-carr, 42% of activity was between 16:00 and 18:00, while about 21% occurred fairly early in the morning between 06:00 and 08:00. Activity was also recorded sporadically throughout the day and night, with 14% captured between 23:00 and 01:00. By April, 72% of activity was in four hours around dusk (i.e. 18:00-22:00), with 21% just before dawn. In sallow coppice between May-July, during the main period of regrowth, 31% of activity was from 20:00 to 23:00, with only 17% occurring during the daytime (i.e. 08:00-19:00).
By setting up trailcams on deer paths leading between the reserve and surrounding farm fields, Cooke was able to establish that the deer at Woodwalton Fen often left the reserve at night to feed, the tendency for them to remain in the fields all night varying from year to year. The cameras also revealed a drop in “traffic” on these deer paths in May, as the grass outside the reserve seeded and became less attractive to the deer and females were approaching calving, which tallied with his deer counts recording a drop in numbers on the farm fields around dusk from April to May.
Camera trapping within the WWF reserve in the summer of 2011 showed the water deer to be active throughout the day, but much like we've seen in Whipsnade animals, their activity was at a minimum around midday. Across two winters on a farm in Buckinghamshire, my trailcams recorded water deer through the day and night during December and January. Watches both on this farm and in Bedfordshire suggest that there is more activity at dusk and during the night, with animals more likely to be found resting/ruminating or grazing during the late morning and early afternoon; even during the rut, when there is more activity through the daytime, there has been a noticeable increase in activity as dusk falls.
Finally, for his thesis on the behaviour of three species of deer (Chinese water deer, Reeves' muntjac Muntiacus reevesi, and Indian muntjac Muntiacus muntjak) for the Freie Universität Berlin, Wolf-Peter Scherpe observed the animals kept in captivity at Berlin Zoo between the start of December 1967 and the end of May 1969. Their activity patterns led Scherpe to the opinion that water deer were a much more diurnal species than the muntjac, something that Centre d'Écologie générale de Brunoy naturalist Francois Feer would also conclude just over a decade later.
Feer spent May and June of 1980 monitoring five adult water deer (two males and three females) kept at Der Grüne Zoo Wuppertal in Germany, publishing his findings in Zeitschrift für Säugetierkunde during 1982. In his paper, Feer wrote how Hydropotes “must be a strongly diurnal species in its natural environment”, because while there was an increase in activity towards the evening, there was no long period of rest during the daytime. He also found that weather affected the pace of activity, predictably less around mid-afternoon in very hot weather and more spaced out activity during cool temperatures. It should be noted that the confinement of these animals, compared with the freedom allowed to the water deer at Whipsnade, may generate activity patterns that are not seen, or uncommon, in free ranging or wild populations.
His and hers
Feer observed that the two males in his small group were more active during the daytime (i.e. 06:00-22:00) than the females, 43% of the bucks' active time was between these times compared with only 27% of the does' activity, and we know season may have a particular influence on activity budgets of both sexes. This is particularly the case in winter, when the species rut, and late spring and early summer when they give birth. In Huxia Park, Fei Yan Ma found the levels of activity to be similar between sexes, with most of the time was spent either resting or feeding. Females did, however, feed for longer than males during the summer, and longer during the summer than the spring; a response to increased energy demands of lactation, presumably.
In line with Yan Ma's observations, at Branféré Animal Park in southern Brittany between November 2002 and July 2005, Christiane and Robert Mauget observed that, for most of the year, does spent twice as much time resting as feeding during the day, the amount of time feeding increasing significantly during lactation. When compared with activity during the anoestrous state, daytime grazing activity was about three-fold higher during lactation and twice as high during gestation, with similar variation in resting durations; 34% less rest during lactation and 16% less during gestation. At Whipsnade, females spent just over half (55%) of their time feeding during summer compared with just under half (45%) in males, which presumably reflected the production of milk having it reached its peak just before weaning. Both sexes spent the least time feeding during the December rut (around 40%), with males increasing time spent feeding to 57% in February. Scan sampling of 10 lactating females held in separate enclosures at Fuyang Chinese Water Deer Farm in Hangzhou by Guoliang Tan and colleagues between July and August 2014 revealed significantly more daytime activity than night-time. Does spent just over 70% of the night resting, while just under 50% of the day was spent the same way. Moving around, feeding, ruminating and engaging in social behaviour was also more likely to happen during the day than at night. Two feeding peaks were observed, 06:00-07:00 and 16:00-17:00, with the peak in rumination following an hour or two later.
The foregoing studies were conducted on deer in captivity, which are significantly easier to collect such data on, and we have little information about the variation in activity in the wild. My observations in Bedfordshire and Buckinghamshire, and those of Lixing Sun on water deer at the Poyang Lake National Nature reserve in China between May 1988 and January 1989, suggest that females in the territories of rutting bucks may spend less time feeding (and resting) than solitary does outside during the winter, largely because they're repeatedly pursued by amorous males. Similarly, territory-holding males will spend much of their time patrolling their territory, scent marking, chasing interloping bucks and hounding females, which reduces the time available for food and rest.