If you’ve already read the article about when roe deer grow their antlers, you will probably know that the mature bucks start growing their head adornments before the youngsters do.

The question is why?

The answer essentially comes down to this: they have an evolutionary urge to dominate to ensure that they will be able to mate with as many fertile does possible, during the forthcoming breeding season.

And they do this by….

Making sure they occupy the best territories

During early spring, adult males will become increasingly cantankerous following their relatively mellow natured winter. If they have formed a loose association with other individuals during the winter (which they commonly do), they will now become very solitary and aggressively spurn the company of other deer, especially bucks.

A mature male will start to spend a disproportionately large amount of time on one particular area of the range; this will become his territory.

He will stake his claim by regularly patrolling along the territory’s perimeter to chase off any other males that may be nearby and to anoint numerous spots (such as prominent sticks and fence posts) with scent secreted from glands located on his head, neck and between his toes. 

These markers will tell other roebucks that this territory is occupied and they would be wise to steer clear.

Mature adults will select the most desirable location, so other bucks will inevitably challenge him to take possession for themselves. 

Therefore, to successfully claim and retain the most favourable territory in the area (somewhere with a plentiful supply of high-quality food, good cover and the least amount of disturbance), the resident beast will need see off his challengers.

Growing antlers prevents battles

When the antlers are still in their growing stage, they are made from non-fully hardened bone and they are encased within a velvety-like sheath, which also covers many nerves and blood vessels that feed into the antler from the skull. 

During this stage, the antlers are sensitive to the touch, therefore, the buck will refrain from head-to-head contact with other males.

As weeks pass by and the number of daylight hours increases, there is a sharp rise in the amount of testosterone released from the buck’s testicles; this has the effect of suppressing the effect of the growth hormone, which was responsible for stimulating antlers’ growth.

At this point, the antlers will stop growing; so, they would have reached their maximum size and the bone will fully harden. The blood supply and network of nerves are cut off and the velvet will peel away, revealing the buck’s crown to the fresh air for the first time.

The antlers’ bone is now dead and is insensitive to the touch. At this point, with a high level of testosterone coursing through his veins and the antlers in ‘hard horn’, the buck is now able to engage in hostilities.

And here’s the important point

The older males shed their old antlers first, enabling their new pair to get a ‘head start’ over the younger males’. Furthermore, since the older males’ testosterone reaches a critically high level sooner than in the youngsters, the mature bucks will be in ‘hard horn’ before any of the other deer; giving them a major advantage in being able to claim the best territory in the range.

Once the less mature males have eventually grown their fully formed antlers, the master buck will be established in the prime spot. And as the dominant beast will have the most plentiful supply rich food sources available to him (because he occupies the best territory), his body will be in better condition than that of his rivals. Consequently, he will win the battle for dominance, putting himself in the best position to mate with the majority of the resident does, when they come into season during the forthcoming rut.

There’s virtually no disadvantage to casting his old antlers before the youngsters’ shed theirs

Back in the preceding autumn, by jettisoning his crown before the younger bucks cast theirs, the master will temporarily lose his dominance over the other males in the area. [Roebucks immediately lose much of their aggressive nature, once their antlers have been cast.]

Of course, that will consequently mean the (normally) dormant beast will be unable to compete with the other bucks to mate with any females that may come into season in the autumn. 

But since the number of does that become fertile in the autumn (during a ‘false rut’) are relatively few in number*, the disadvantage of shedding his antlers before the youngsters do, is a small price to pay for the significant advantage of being first into ‘hard horn’ in the following spring when the season’s territories are established.

*In addition, the master’s testes would have stopped making sperm before the less mature males’ testicles (because the youngsters’ sexual development starts later in the year), so the older beast is less likely to be fertile in the autumn.