Do deer mate for life?
In a word, no, deer don’t mate for life, and here's why...
Just to be clear: a lot of the information contained on this website relates mainly to roe deer, and that is certainly true for this piece. Some of the information in this post does, indeed, relate to deer in general, but as far this article is concerned, roe deer are the focus.
The does’ short window of opportunity
Deer come into oestrus (become fertile) once, maybe, twice a year. And the time in which they’re on heat is just 2 to 6 days.
To understand why roe deer often have more than one mate in a breeding season, it’s helpful to understand the forces which instinctively drive them.
After a female roe has her needs met for food, shelter and warmth, she will feel the urgency to produce offspring (when she becomes fertile) and successfully raise her fawns, once they’ve been born. Like all mammals, apart from survival, it’s the driving force in her life.
Since a female roe deer will only be fertile for such a relatively short period of time in the year, she will be very proactive in finding any suitable roebuck to fertilise her ripe ovum. This is why does may mate with more than one partner during an oestrus cycle; the urge to procreate is very strong.
Competition between the bucks
All healthy roebucks, over one year of age, will be fertile during the rutting (breeding) period. So, in most roe deer ranges, there will be a number of males that will make will make a suitable mate for a doe on heat.
At the moment, I’m not aware of any widely published evidence to suggest that a female roe deer in oestrus will show a strong preference to mate with one particular type of buck. Although I wouldn’t be surprised if such work was forthcoming in the future, especially now that we know that female fallow deer can select their mating partner. *
A rutting female will have buck enticing pheromones streaming out from her bottom, which will attract virile males from all around. But the territorial nature of roebucks means that it’s the dominant beast who is very likely to be the male that is likely to court and eventually couple with the amorous doe. However, there is a peak in the rut around the end of July and the first part of August, so, not all does come into heat at the same time.
The fewer number of females that are currently receptive, more likely it will be that it’s the master buck will be the one that mates with the willing doe. (He able to chase off competing males.)
In an area where a given adult buck reigns supreme for a few years, it could appear that the does are mating with just one individual buck. However, this would be misleading.
Dominant bucks expend much energy staying close to their suitor, since if they were to become separated, she is very likely to mate with another nearby willing male, which will be waiting in the fringes of the ruler’s territory.
Roebucks engage in savage fights in their bid for dominance and as a result some will die in battle, or from their wounds, so there will be turnover in the position of king roebuck of the area (and also not least because humans have the habit of hunting the biggest and most impressive specimens in a given area).
So, the dominant buck one year, will not necessarily be the ruling male the following rut. (And during any one breeding season, it’s the dominant buck that will service a disproportionally large number of the does.)
Parental females need little from the bucks
The bucks play no part in the raising of their young, so the does form no allegiance to the father, apart from a loose association that can occur outside the period of male territoriality.
The main thing a female roe deer needs from a roebuck, is for him to fertilise her eggs when she’s in season. She is fully able to raise her young, from being a tiny fawn hiding in the long grass, through to being an independent yearling.
[* Dr Alan McElligot, Dr Mary Farrell and Dr Elodie Briefer from Queen Mary, University of London, University College Dublin and UWE Hartpury have discovered that not only do female fallow deer breed with more than one mate, but also, decide with whom they’re going to mate with.
This behaviour was explained by the females using a strategy that maximises the probability of them becoming pregnant. It was said that the does would be most likely to mate again if her first partner had already serviced several other females, or if the mating buck was an old specimen.
In both of these cases, the number of sperms entering her body may not be enough to fertilise her ovum and by selecting different mates and mating more than once, will lead to an increased chance of becoming pregnant.
It is advantageous for the female deer to be fertilised during her first oestrus, since a delay in the fertilisation of her egg by 3 weeks (when a second oestrus would occur, if the first one was not successful), would cause the resulting fawn to be born later than normal; youngsters from a late birth have a lower chance of survival.]