What Happens After A Deer Leaves Its Mother?
In spring roe deer fawns leave their mother.
The first to go are the bucks, when their testosterone levels rise and they feel the urge to explore and, ultimately, to take control of a territory – although claiming a territory is very unusual in a roebuck’s first year away from their mother.
Females generally leave later than the males, as they are driven away by their increasingly cantankerous mother, as she prepares to give birth once again. In addition, does don’t normally venture as far away from their former home range as the bucks.
This seasonal movement of deer away from their natal grounds is called dispersal.
Initial Dispersal Is Often Not Final
It is important to understand that this dispersal of immature roe deer away from their former home is not, as many sources suggest, a one-way journey. As we shall see, this process of parent-offspring and sibling separation is a complex one, and various forms of associations between the deer can exist for well over a year after the youngsters’ first birthday.
Studies by Dr. John Linnell in 1994, working on his PhD thesis at the National University of Ireland, obtained some very interesting data relating to the average separation of roe deer between mothers and their offspring. Using radio-collared mothers and their fawns, the following data was obtained for a population roe deer residing on the Norwegian island of Storfosna.
Time Distance in metres between mother and offspring
June/July/August 79 (Male), 96 (Female)
Sept/Oct/Nov 59 (M), 73 (F)
Jan/Feb/Mar 83 (M), 158 (F)
Apr/May 210 (M), 156 (F)
June/July/August 1651 (M), 775 (F)
Sept/Oct/Nov 1250 (M), 214 (F)
Jan/Feb/Mar 683 (M), 302 (F)
Apr/May 1658 (M), 827 (F)
June/July/August 1592 (M), 671 (F)
Sept/Oct/Nov 1089 (M), 490 (F)
(Although these figures relate to a population of roe deer on a Norwegian Island, the general pattern is applicable to any roe population living in a non-mountainous woody / agricultural region.)
As you can see, the fawns stay relatively close to their mother during their first year of life and at least 40% (this figure is derived from other data) move away from the parental doe during their second year. But many return in the autumn and winter.
In the following spring (their third year), at least 80% of the males will vacate their mother’s home range (many permanently) and about 40% for the females (roughly the same for their second year).
The actual percentages of how many deer stay and which individual deer depends on many local factors, see further down this post.
Roe Deer Are More Social in Winter
Less food and a steep reduction in the males’ testosterone levels, means that during the latter part of the season, roe frequently gather in small groups. And this often results in a mother’s offspring (particularly the females) returning to her home range during the winter.
And Here’s Why
From November through to the following spring, food in the woody areas (the roe’s preferred habitat) runs low. However, there’s often still sufficient food available in the more open areas, especially in agriculturally rich regions.
For this reason, roe deer are often seen feeding in and around open areas of grassland, winter crops, etc…
However, there is a problem with that: being out in an open area makes the deer far more visible to predators.
So, here’s the solution to this problem… they gather in groups; the increased vigilance of a group of deer reduces their susceptibility of predation in open areas.
Even though adult roe have no natural predators in the UK (with the exception of eagles in Scotland), they are genetically hard-wired to adopt the same antipredator behaviour which has allowed them survive in places where there are significant numbers of wolves, lynx, bears and golden eagles, all of which are known to prey on roe.
But the advantage of having an increased number of eyes periodically keeping a look-out for signs of danger*, brings with it the disadvantage of having more hungry deer in close vicinity to each other, thereby increasing competition for food. (*In a social setting containing mixed year groups of roe, it has been shown that the adults are far more vigilant than the youngsters.)
Also, being in such close proximity of others of its own kind can induce fractious behaviour.
And That Bring Us Onto The Next Important Point…
Deer tend to gather in small family groups because close proximity to parents and siblings is tolerated more often than mixing with non-related roe. And this is most applicable to roe in their first few years of life.
Increasing age brings with increased life experience and size (until maturity), so an individual deer is more likely to be able to mingle with non-relatives as they get older, particularly for bucks. Females normally stay in family groups because they get older, they tend to have their own fawns to care for.
In old age, roe deer tend to be solitary at all stages of the year, except during the rut, or when a doe has dependent young.
Why Roe Deer Are Normally Solitary
For much of the year, there is sufficient food in and around their preferred woody areas to sustain them. And in this bushy type of habitat where there are many branches and fallen tree trunks to negotiate, unless a predator can get very close, the long, spindly legs of a roe deer give it a distinct advantage when it comes to escaping danger.
But this type of habitat, the presence of a large group of animals would make initial detection easy for a predator and, when individuals get in each other’s way when they flee, the odds start to swing in favour of the predator.
So, when there is abundance of available food and considerable vegetative cover, roe deer are solitary.
Why Do Roe Deer Leave Their Mother’s Home range?
There is no simple explanation as to why this happens, the situation is complex and many local factors will an influence. However, the following will be important:
Competition for food, shelter and mates.
The need to avoid inbreeding.
The males and females leave their former home for different reasons, so each will be discussed separately.
But before we look at the dispersal rates of the bucks and does, it is important to consider the carrying capacity of the land; which is essentially linked to how many healthy roe deer can be sustained by the habitat’s resources, such as food and shelter.
If you consider an environment where there is an abundance of nutritionally rich food and plenty of woody / bushy type of cover, the dispersal rates are going to be low, particularly for the females (see the section on female dispersal below).
Conversely, the dispersal rates for comparatively poor habitats are high, since there is unlikely to be much excess capacity to support more roe deer.
Much also depends on body condition of the deer, too.
The better the physical condition, the more likely it is that yearlings and subadults will move off to pastures new. This is because moving away from their natal range is costly in terms of energy, so prime conditioned individuals have a tendency to successfully change their home range.
Adult European roe deer typically weigh anywhere from 10 to 25kg, depending on sex and the richness of the habitat. A 10% increase in body mass over the average for the roe population in a given location, is enough to constitute ‘good’ physical condition.
For a yearling to undertake dispersal, 15 kg is considered to be the minimum body mass needed to successfully vacate their former home range.
Dispersal of Male Roe Deer
The main reason for this is competition for mates.
For approximately 6 months of the year, March to September, adult roebucks are territorial. Which essentially means that they will spend the vast majority of their time in one particular area of the range, and defend it by marking numerous spots with their scent and scrapes, as well as confronting intruding bucks with agonistic behaviour.
This agnostic behaviour takes the form of threat displays and physical combat (fighting) to see off any challenges to his domain. And it’s this aggressive behaviour of the larger, stronger adult bucks that causes the dispersal of the young males.
But interestingly, not all juvenile bucks are equally likely to move away from their natal range. In 1994 Hitta Kjell Wahlström working with Stockholm University discovered that the young roebucks most likely to disperse are the ones with a particularly well-endowed head.
Wahlström reported that the males with the largest and most impressive antlers usually have a larger body mass, compared to the average yearling. (Larger than average deer have been shown to grow bigger than average antlers, even after their body mass has been taken into account.)
Their relatively large physical stature poses an obvious threat to the resident master buck*, who claims the best territory in the area.
(*The reason for this because impressive antlers is an indication of large testes, which means greater sexual maturity. Therefore, the well-developed youngster would pose a significant threat to the dominant buck being able to impregnate as many females as possible, during the rut, to pass on his genes.)
The dominant beast subjects all well-antlered juveniles to far more harrying, than the less well-developed males. Hence the larger than average subadults are evicted from the master’s domain.
Dispersal of Female Roe Deer
Females are not territorial in the strictest sense of the word, but it is not unknown for adult does (especially those with dependent fawns) to dole out hostilities to other females encroaching on the core area of her home range.
On several occasions I have seen a few adult does use combative behaviour to see off a female interloper. In fact, remote cameras left in bushy areas known to be frequented by certain roe have recorded two adult females engaging in head-to-head combat, not dissimilar to have seen with the bucks.
But although antagonistic behaviour does sometimes occur between the females, it is not observed often enough to the main reason to account for the dispersal of the females.
As they are far less aggressive than the bucks, the does distribute themselves around the area according to resource availability.
The young does will spread themselves around in such a way that each female has sufficient food, shelter and disturbance free woody cover.
In conclusion, the seasonal movement of the does is undertaken to secure an ideal living environment for them and their fawns, rather than being forced out their natal range by an aggressive adult, as in the case for a young roebuck.
How Far Do Roe Deer Move?
This depends on the environment in which they live.
Generally speaking, the poorer the habitat, the further the animals will have to disperse to meet their living requirements.
For example, in regions where their environment is very rich, like the agriculturally developed regions of Europe, the average dispersal distances are in the range of 0.8 to 3km, although or course, there are a few instances of much longer distances being covered.
However, there are great populations of roe deer living in north eastern Russia (the Siberian roe deer), and their habitat is one of boreal forest, which experience significant seasonal changes in weather.
In the winter, their home becomes depleted in terms of available food, primarily due to extensive deep snow cover. And in these areas, dispersals up to 100km* have been recorded by researchers by G. Cederland and O. Libery using radio-collar tracking. But most disperse much less than this, usually about 20km. Far enough to get to an area where the snow is not deep enough to prevent free movement (i.e no deeper than 50 to 60cm) and does not obscure their food.
(*The relatively large weight of Siberian roe allows the deer to have the ability to undertake such long migrations.)
Some Are ‘Stayers’, Whilst Others Are ‘Leavers’
Even within a given population of roe, whether they are deer in an agricultural region or in a boreal forest, there are certain groups that appear to have a predisposition to move out of their birthing range, rather than stay.
Researchers Wahlström and Libery put forward a suggestion that there could be a genetic explanation to explain the propensity of some roe deer to disperse more widely than others.