What happens during a deer's first year of life?
A roe deer’s first year is an interesting one, and it’s the main topic I’d like to deal with here. As you'll discover below, the adroit behavioural characteristics of a fawn's mother, are central to her offspring's chances of survival
In fact, the first year of a roe deer’s life is crucial; not only for the individual deer itself, but also for the significantly important influence it has on the population dynamics it has on the whole local population. When it comes to considering the numbers of roe deer on a local basis, the rate of fawn survival is far more important than the reproduction rate of the resident females (does).
When do roe deer give birth?
In general, most of the pregnant does in a given area tend to give birth within 3 to 4 weeks of each other, with the average birth date can be anywhere from late April, through to mid-June.
There is some latitudinal variation with deer in lower latitudes giving birth earlier in the season than in more northerly areas. There’s also longitudinal difference too, with western populations birthing earlier than roe in the east. But the important variable is not the global position per se; it’s the arrival of the correct state of the season that is the key factor.
Typically, does in southern Spain give birth in late April and Sweden and Denmark fawns being born in June. Mid to late May is a common time in southern England.
Even though in any one year, the births do tend to be grouped into a time span of 20 to 30 days, the actual period of birthing is not same every year. Local weather conditions do have a bearing on the timings, with a late spring possibly delaying the period of maximum number of births by a couple of weeks.
Why do births occur roughly at the same time?
Although this looks like the birthing within the local roe deer community could be synchronised, it’s unlikely that the mothers have all ‘decided’ to give birth at the same time to reduce the chances of their youngster(s) being taken by predators. The most plausible reason why most of the does drop their fawns within a month’s window is that birthing is timed to coincide with the optimum environmental conditions, to ensure effective cover for hiding their fawns and an abundance of natural food for them to feed on, enabling them to produce a plentiful supply of nourishing milk for their babies.
Late arrivals will experience a shorter time when the food is of optimal quality during their crucial first summer, and therefore their overall growth will be compromised. If the young are born too early in the season, the quality of the vegetation will be poorer, meaning the mother will be less well-nourished during the latter stages of pregnancy and the it will more difficult for the doe to produce copious amounts of high-quality milk for her young. In addition, inclement weather exposes the fawns to an increased risk of hypothermia.
Roe deer are a hider species
This means that during the period of time when the young are especially vulnerable to predation (i.e. their first six weeks), they they use a survival strategy of hiding their fawns in the long vegetation to reduce the chances of foxes and other predators finding them. And in the meantime, the mother will wander (on average) anywhere from 50 to 200 metres away (although distances in excess 1.5 miles have been reliably recorded) from their youngster to fed and rest.
The hiding behaviour of young roe deer relies on reducing the detection radius (how far away a predator can detect a prey animal). Fawns carry very little scent and their mottled coat along with their propensity to freeze when faced with danger in the first 40 days, can reduce detection radius to less than 1 metre.
Along with the difficulty of detection, the hider behaviour of young deer is very effective a few other reasons:
Firstly, since the detection radius is so small, the predator will have to expend a lot of time searching for prey, which is not energetically favourable.
Secondly, because mothers tend to change the location of their vulnerable youngster every night (typically from 75 to 200 metres), ‘hotspots’, where predators get to learn where they are more likely to find prey, do not develop.
Therefore, areas were searched one day and were found to be barren of prey, are just as likely to contain a fawn the next day and will have to be searched again.
Thirdly, since mothers tend to move a significant distance away from hidden fawn, their presence and behaviour will not unduly drawn attention to their susceptible young. Enabling the parent to reduce energy expenditure by not having to chase away foxes, and also to increase the time on foraging. In addition, since she is not tied to close proximity of her baby, the doe will have the freedom of being able to move around her fawning range in such a way as to locate the best quality food, which will increase the nutritional content of her milk.
As previously mentioned, although the female can be found quite a distance away from her youngster, mothers normally stay relatively close during the first 10 days; enabling them to frequently reinforce their pair-bond, which is essential to keep them together during most of their first year. During the 10 days of their life, fawns are only active for about 10% of the time, and the vast majority of this time is when the mother is present. The rest of the time is spent sleeping and generally resting; movement is kept to a minimum.
After 10 days, the mother will wander further away, but around 30 days after birth, mothers will reduce the distance to their hidden fawn again. And this starts to coincide with the time when the youngsters will flee, when they detect the close proximity (with 10 metres) of a predator. Once a fawn reaches a stage where they will be flushed from cover, rather than lying doggo, they never do back to the freeze response to approaching danger.
Fawns forming part of twins or triplets are usually not hidden close to each other during the time when the youngsters freeze in the face of danger; distances of around 30 to 60 metres are not uncommon at this stage. After that, the fawns often lay very close together whilst resting, sometimes even touching each other.
Where are fawns located?
The place where the fawns are deposited by their mother is called the bedsite location, and the main things that are needed for suitable bedsite location are seclusion and vegetation cover, to obscure the youngster.
Prevailing weather conditions are also likely to play a significant influence, too, in order to reduce unnecessary energy expenditure to maintain the correct body temperature. So, keeping out of strong winds and direct sunlight, as well as a dry substrate are important.
In wooded locations, spots with dense shrubs and fallen trees are favoured. More open areas, I have found long grass is preferred.
Even though female roe deer at this time of year are especially keen on locating and feeding on only the most nutrient dense food, the babies themselves are often found in relatively poor vegetation (from a food source point of view). Old, scrubby vegetation is harder for predators to detect the vulnerable youngsters, so because the mother doe has effectively hidden her fawn, she is able to wander away for a quite a distance to the best local food source.
It’s essential that the doe feeds on the rich food sources, so she can maintain a constant flow of nutritious milk (as well as build up enough energy reserves for the forthcoming rut).
Researchers state that, relative to their body mass, roe deer administer the highest level of care for their youngsters than any other well-understood deer.
After the summer’s rut
There’s now a major change in the fawns’ behaviour. After the middle of August (ie post the rut), the young deer are much more mobile than they were before. No longer will they hunker down and hide when confronted by a dangerous situation, instead, now they (along with their mother, if she’s close by) will sprint away in classic roe deer fashion; bounding through the woods or across the land, with their bottom fluffed up in alarm.
Whereas before the peak of the rut, the fawns spent much of their time out of sight and away from their mother, now, the doe and her young spend much of their time within a short distance of each other, as move, feed and rest throughout their home range.
Autumn and winter
As the days get shorter and the temperature drops, the fawns continue to stay close to their mother. Youngsters are guided by the doe to safe places to find shelter, rest and eat.
The deer living in open areas, often form loose associations with other roe, including adult and sub-adult bucks, who lose much of their aggression, as they become non-territorial after the heat of the rut.
The fawns’ danger period
Towards the end of winter and into early spring is the time when fawns’ are most likely to die of natural causes.
The main reason is this: Because of the scarcity of rich food sources during the winter months, all roe deer possess their lowest body fat percentage at this time of the year. And for the youngest individuals, that is likely to be around 1.6 to 2%; if it drops below 1.5%, they’re probably going to die.
So, if it’s a long, hard winter and nutritious food sources are relatively few and far between, a young deer’s body fat could drop below the critical level and premature death will occur. The chances of this happening are exacerbated by competition from other deer, as well as if their spring moult starts early.
Small deer are especially susceptible to the adverse effects of cold, wet weather (especially driving rain or deep snow) because of their body’s high surface area to volume ratio, which essentially means they lose heat easily. So, it is very energetically demanding for the fawns to maintain a healthy core temperature, resulting in a draining of their vital bodily fat reserves, which also acts a thermal insulator.
Assuming the fawn is healthy, males start to grow their first proper set of antlers from the latter part of winter and into spring. (Some, but certainly not all grow tiny antlers during their first autumn and winter. These are called button antlers, and are shed before the ‘proper’ pair grow.)
Fawns leave their mother
In the spring, the young deer become yearlings and they leave their mother. This is called dispersal, and it’s the young roebucks that separate from their mother first. The young does sometimes stay with their mother almost until the adult gives birth again.