Red deer are active over the full 24 hour period, but exhibit both crepuscular and seasonal peaks in activity, with their longest periods of activity at dawn and dusk (the term crepuscular is derived from the Latin crepusculum, meaning “twilight”). Studies of radio-collared deer in the Slovak Republic (Central Europe) have found that these animals spend anywhere between 20% and 90% of their time feeding, according to season, then reducing their activity during the late winter months (January and February). The same study also found that there was about a 60% decrease in heart rate during winter (compared with summer peaks) and documented a previously unknown case of nocturnal hypometabolism (i.e. where the deer reduce their metabolic rate at night to cut their energy expenditure during winter) in this species – the deer achieve this by lowering the temperature of peripheral body tissues by 10C (50F) or more over the daytime highs, which reduces heat loss.
It seems that the majority of the variations found in the deer’s metabolic rate over the year could be linked to the heat increment of the vegetation available to the deer as food. When an animal eats something, it generates heat in the process of digesting it and it is this increase in heat production following the consumption of food that biologists call the heat increment. The authors of this study, which was published in the American Journal of Physiology during 2004, wrote:
“…the approximately twofold difference between the annual maximum and minimum of daily mean heart rate corresponded well with the also twofold higher protein content of natural deer forage at the summer peak compared with the winter low.”
Passing the time
With the exception of the stags during the rut, the bulk of a deer’s time is spent trying to find enough food and, as such, their activity patterns are intrinsically linked to the food available to them. When the rumen is full the deer cannot eat anything else and they must stop feeding and start ruminating. Red deer exhibit a feed-ruminate cycle of between five and nine hours, depending on the type of food taken; this results in a clear pattern of activity, cycling through periods of feeding and periods of ruminating.
Red deer living in open hill areas (e.g. Scottish Highlands) tend to exhibit a pronounced activity cycle: they spend much of the day at high elevations resting and ruminating (in some seasons elevation may help reduce irritation from biting flies – see below), descending at dusk to feed during the night, before returning up the hillside at dawn. Deer inhabiting woodland have a similarly pronounced cycle, whereby they spend the daytime in, or close to, tree cover where they rest and ruminate (there may also be some browsing) before moving into more open areas (e.g. meadows, clearings and agricultural fields) at dusk to feed. Studies of Red deer in Scandinavia and New Zealand have found that they are more nocturnal in areas of high human disturbance.
Deer of both sexes can also be seen wallowing in mud holes during the daytime; this is especially true of stags during the rutting season. The activity level of males increases considerably during the autumn rut and stags will typically rest, eat and sleep little (if at all) during this period. Indeed, time budget studies suggest that feeding may account for less than 10% of a stag’s activity during the rut.
Overall, the level of activity during the rutting season, which runs from the end of September to the end of October, will depend upon prevailing weather conditions (inclement weather can reduce activity considerably) as well as population density and levels of disturbance. Stags on the island of Rum, for example, represent a high-density population that is subject to little human disturbance (culling is prohibited on some areas of the island) and as such the competition for mates is high and rutting stags will not generally eat or sleep all the time there are hinds to be coveted.
In more disturbed places, such as the New Forest in Hampshire, where culling pressure and human disturbance results in small populations of deer, there may be few suitable challengers and the rutting stands can be monopolised by a single large stag – the lack of competition means that it is not uncommon to see the stag resting and feeding with the hinds, breaking off only to chase away interlopers. In situations where competition with other stags is low, rutting males tend to bellow less than conspecifics in locations where competition is high.
Contrary to popular misconception, deer do sleep, although not in the same manner that we humans do. The electrical chemistry of the brain during rumination is similar to that of (mammalian) sleep, meaning that they can stay ‘awake’ chewing the cud, with their eyes glazed. There are times when ‘genuine’ sleep is necessary, however, and according to Pennsylvania wildlife biologist Kip Adams, a typical bout of sleeping includes:
“… 30 seconds to a few minutes of dozing, followed by a brief alert period, and then more dozing followed by an alert period. This cycle often lasts for about 30 minutes. Generally, once per 30 minutes deer will stand and stretch and they may urinate or defecate before laying back down.”
During periods of rest, which may account for 50% to 60% of their time during winter and 40% to 60% during summer months, the deer remain bedded down at sites for which they may have considerable fidelity. Between June 1999 and December 2000, a team of French biologists monitored the activity patterns of seven wild adult Red deer—in the Le Parc National des Cévennes (southern France)—that had been caught and fitted with GPS radio collars.
The researchers found an interesting duality in bed site choice by the deer: the animals appeared to be facing a choice between availability of feeding sites and sufficient cover. During the daytime, the deer opted for sites with greater cover, while at night (when the deer were less affected by disturbance) the deer could be less selective and chose resting sites with more variable characteristics. The study, which was published in the European Journal of Wildlife Research during 2008, also found that the deer resting bouts were shorter during the night than during the day from June to October – both sexes reduced their resting activity during the rutting season. There was no significant difference between the resting bout lengths of stags and hinds, although hinds tended to use steeper slopes than stags, presumably because these were less disturbed than more open habitats.
Disturbance seems the key factor in explaining deer bedding site choice, because work on the undisturbed populations of Rum by Cambridge University and Edinburgh University biologists demonstrates no occurrence of such variations in day and night time rest site. Moreover, recent work by researchers at the Northeast Forest University in China has found that Red deer in the Wandashan Mountains of northeastern China avoided human-altered habitats (e.g. villages and forest roads) for movement, bedding and foraging because of disturbances during late winter – bedding sites were sensitive to disturbances from humans and other ungulates. The scientists also observed that the deer chose ridges and slopes with a south-eastern and southern exposure as bedding sites during the winter; these were presumably selected because of their warmth and might thus offer energy savings to the deer.
It is also worth mentioning that deer lying down may not be either sleeping or ruminating; they may be trying to avoid biting flies. In an interesting paper to the journal Behavioral Ecology and Sociobiology back in 1979, Yngve Espmark at the University of Trondheim and Rolf Langvatn of the Norwegian State Game Research Institute reported that resting times of captive Red deer at the Songli Research Station, central Norway, were more than twice as long on days when fly harassment was severe. Earlier work by English ecologist Fraser Darling during the 1930s had established that tabanid flies (horse flies) can have a profound impact on the activity patterns of Red deer, with outbreaks causing, among other things, changes to the spatial organization of the social groups; Espmark and Langvatn found that Hydrotaea irritans (see right), the so-called ‘head flies’, can also take their toll.
The biologists observed that on days when fly harassment was estimated as nil, the deer spent 33% of their time lying down; this increased to 71% on days of severe fly harassment. It seems that, when the deer laid down, the number of flies hanging around dropped, probably (the biologists argue) because a resting animal is less attractive than a moving one, perhaps because it has a lower body temperature, is breathing out less carbon dioxide, perspiring less, and so forth. Logically, lying down may also reduce the surface area of the body available for flies to bite.
To move, or not to move?
Recent tracking data have suggested that, over some parts of their range at least, Red deer movements are highly seasonal. In a paper to the European Journal of Wildlife Research during 2009, Dominique Pepin and two colleagues—all at France’s Institut National de la Recherche Agronomique—presented the data from their monitoring of Red deer fitted with radio collars in the Cevennes National Park in central France. Unfortunately, the biologists were only able to trap four Red deer (two stags and two hinds) so it is difficult to draw many conclusions from their study, but the GPS data do, nonetheless, make interesting reading.
Overall, the hinds moved greater distances than the stags (although the stags tended to move further during the night); it seems that there is only a short period during the year when female walking activity is drastically reduced and this is during the rut, when they are found on the rutting stands. The females were most mobile between the hours of 15:00 and 18:00 and least active during the night (between 21:00 and 03:00). The stags exhibited peaks of increased walking at 06:00 and 18:00.
Pepin and her colleagues noted that males moved around least between November and January, having been most active during the rut; the authors suggest that the change in the weather, with average minimum temperatures of 0C (32F) at the study site may be the cause as the deer moved around less to conserve energy. Males have lower body fat reserves during this time of the year, having been engaged in the rut during much of September and October and so may be more sensitive to changes in weather (and specifically temperature) than females. This seems apparent in the dataset, which show females active throughout the winter until the end of February, when walking activity declined. Overall, the authors concluded:
“The walking activity of males peaked during the rut whereas that of females decreased. But compared to males, females moved more both during winter and daylight hours.”