The Roe Deer Annual Rut

The hottest months of the year stir up the reproductive instincts of one of Britain’s earliest inhabitants. The months of July and August bear witness to the Roe deer annual rut. Typically timid and secretive, the Roe deer is more visible during the rutting period.

The long days of these summer months hold the promise of more frequent sightings to the enthusiastic observer. However, we would do well to understand Roe deer behaviour to ensure successful sightings without disturbing nature’s work in progress. Learning about the Roe deer’s mating strategy, behaviour and communication are all key here. Do you want to observe these secretive animals in a less intrusive way? Read on to gain insights into the hidden world of this ancient if diminutive deer.

Evolution

Roe deer first appeared in European fossil records 10 million years ago. Indeed, sites in Britain reveal that Roe deer were here at least 600,000 years ago. Roe deer evolved alongside predators such as the European Jaguar, European Hunting Dog, Lion, Spotted Hyaena, ancestors of the Wolf and Cave Bear. With the onset of glaciation their British habitat was largely under ice. So they moved south over a land bridge to mainland Europe. As the ice retreated the Roe deer returned along with other animals. That is until Earth warmed sufficiently for the land bridge to disappear under rising sea levels.

The first post-glacial records of Roe deer date back 10,000 years from a site found at Thatcham in Berkshire. It has survived while others of its pre-historic contemporaries have perished. The Roe deer thrives once more in mainland Britain after almost being wiped out due to hunting. Every summer this highly adaptable relic of the Pleistocene which is equally at home in our post-industrial agricultural landscape as in ancient woodland, continues to breed unabated.

Timing Of The Roe Deer Annual Rut

The Roe deer’s summer breeding season is a unique phenomena amongst British deer. In fact, this is related to another unique evolutionary trait of Roe amongst deer – embryonic diapause. This temporary pause of embryonic development suggests a selective advantage. Delayed implantation is a widespread lifecycle strategy in birds, fish, insects, plants, and mammals. Ecological factors promoting survival of the young determines the timing of births. This in turn sets limits on the timing of the mating season.

Delayed implantation may have evolved when optimal times for mating and birthing were separated by more than a gestation period. For example, a long winter would reduce opportunities to find mates. Delayed implantation provides the reproductive means to mate during the summer. Summer is the season with the greatest possibilities for female choice or male competition when living in the seasonal environments of the northern hemisphere.

Territoriality

Male Roe deer are seasonally territorial: they will claim and defend their territory from March to August. There is a tendency for males re-establishing old territories to be first. They will only establish and maintain a territory when they reach three years or older, although the male becomes sexually mature by the age of one year.

Territory size, location, and habitat quality are characteristics determining the number of potential mates that a territorial male can monopolise within its area of dominance. Males usually compete strongly to establish and defend the best territories. The ideal territory provides access to females, food and cover. As such these territory characteristics are very important sexually selected traits.

Low Risk – Low Gain Strategy

Territoriality is as a “low-risk low-gain” breeding strategy. The success of a territorial mating system based on relatively little investment during one breeding season is dependent on a high probability of being able to defend a territory over several seasons. Roe bucks show a very high degree of fidelity to their summer territories. They will defend the same territory in consecutive years if they survive the intervening winter.

Roe bucks may demonstrate an “always stay” approach in order to gain the benefits of site familiarity. Intimate knowledge of an area is likely to increase feeding efficiency, improve predator detection and escape behaviour. The lethal nature of their antlers and the low levels of physical contact suggest that Roe bucks follow some type of “resident always wins” rule in fights. This makes the strategy more plausible. Indeed, fixed territory boundaries can outlast the occupancy of any single individual.

The Impact Of Territorial Behaviour

The Roe deer’s long territory occupancy compensates for the relatively low amount of energy invested in mating each year. This is in stark contrast to other deer for whom tenure time is measured in weeks or months, rather than years. In species such as the Red deer or Fallow deer, the females congregate together in large herds. Herds provide the potential for significant mating rewards for a triumphant stag. The stable, scattered and solitary distribution of Roe deer females means that such breeding bounty is not available to a dominant Roe deer buck. Female distribution and behaviour determines male spacing behaviour. In the case of Roe deer, females occupy similar size home ranges to males during the annual rut. This constrains potential polygyny levels. Thus there is little to be gained by excessive energy spent on mating within a given season.

Female Rutting Behaviour

Females are monoestrous (one breeding season a year). A female can go into oestrous any day during the mating period. During that period the female sends messages to all males in her vicinity and males respond by walking to the female’s location unless they are already attending another oestrous female. The doe has a short period of receptivity – approximately 36 to 48 hours. Although females actively choose their mates, we know little about how they decide which mate to choose.

However, we can observe that female Roe deer may undertake short excursions, outside of their normal home range, to visit neighbouring male territories. They can even wander over several territories to find a mate.

This behaviour may be motivated by a desire to select a partner of superior quality or in order to avoid inbreeding. Alternatively, the male present on the female’s home range could be already engaged in courting another oestrus female. Since Roe deer females are monoestrous, with a short period of receptivity, the excursions could be the result of a search strategy to find a free male. Among well-studied ungulates, this behaviour appears to be unique to Roe deer. This is perhaps because of the marked male territoriality in this species.

Male Rutting Behaviour

During the Roe deer annual rut the buck’s testosterone levels are at an annual high (TBC), his testes have enlarged and his reproductive anatomy has developed to enable him to mate. When a male is attending an oestrous female, he follows her closely wherever she goes which does not leave much time for other activities. So it is no surprise that bucks can succumb to exhaustion during this guarding period. Only after the male satisfies the female with his mettle, will they mate.

A buck in his physical prime with impressive antlers stands the best chance of breeding success. Antler size is a trustworthy indication of male quality. Antlers advertise the genetic and environmental (phenotypic) influences on the individual. The size of antlers is dependent to a large degree on diet. A fertile habitat which provides the buck with a protein (and mineral) rich diet during the antler growing period (winter and early spring) will give the buck the best chances of growing thicker, longer antlers. Females might assess antler size to judge male strength, reproductive condition and genetic quality – as well as the quality of his habitat.

Males can successfully breed as young as 2 years of age. However, only subadult bucks fit enough to defend a territory mate. Breeding success tends to decrease in old age, as senescence coincides with a loss of territorial dominance.

Courtship Displays

The courtship displays are markedly different to the other displays (status, dominance, threat, submission and alarm) of Roe deer. The male approaches the female with neck and chin outstretched. The female urinates and the male responds with a flehmen grimace after sampling the female’s urine. The doe entices the buck to chase and the male follows the female closely – sometimes in a ring around a tree or other prominent feature. The female may respond to the interest of a male playfully or display token avoidance. When the female is ready to copulate, she will stand motionless while the (exhausted) male mounts.

Vocalisation

Females squeak to attract a mate and squeal when they are being chased. Males make a harsh, grating noise when chasing an oestrous female.

Scent

Scraping and rubbing is one way for Roe deer to convey scent communication. Males perform these types of scent marking during the territorial season. By using one of their front hooves to paw the ground they are able to transmit scent from their interdigital gland. By scraping and rubbing their antlers against vegetation they can spread scent from the glands on their head. Scrapes play an important role in establishing and maintaining territory. Although their primary purpose is to communicate territorial ownership between males, females also gain information from these scent markings on the status of males during the rut.

Respect for Rutting Deer

The normally cautious Roe can become so focused on mating that they let their guard down. Although it is possible to get closer to buck in particular during the Roe deer annual rut, this human proximity inevitably results in alarm and the courtship will stop. Deer that are surprised at close proximity will flee immediately without barking. Deer standing at a distance from an observer will bark repeatedly, adopt an alert erect posture, stamp with a forefoot, leap in flight or freeze (often with one leg raised). Unnecessary interruptions can be avoided by watching the deer’s natural behaviour from a distance using binoculars or a telescope. Only then will the lucky few witness the act of mating by one of Britain’s oldest inhabitants.

Author: Tim Plowden

Editor: Reehana Shihab