Rutting Impalas: Boys behaving badly

By Chad Cocking

“Shhhhhh! What is that sound?” is a commonly heard line at Tanda Tula Safari Camp at this time of year. This question is usually quickly followed by a dimming down of talking as all the guests strain their ears to hear what one of their travel companions has heard. Suddenly a vicious, guttural roar comes emanating from the nearby bushes and all eyes open as wide as saucers as someone states: “It’s a lion!”.

As guides, we swiftly calm the situation down. Everyone’s eyes return to more normal proportions, and we inform them that the roaring sounds they are hearing are nothing more than hormone-driven male impalas making their masculine-presence known to the entire impala world. Despite their appearance, these quiet-looking bovines can put on quite a raucous, anything-but-antelope-sounding, display when they need to impress the ladies.

May is the middle of the impala rutting season. It is a unique time of year to watch these often overlooked antelopes in the throes of the busiest part of their annual social calendar. Usually peaceful and calm, the rising hormone-levels in the impala males evoke a level of behaviour not shared by any other male antelopes in the Timbavati, and so it is very interesting to view these antelopes.

Impala are the most abundant and widespread of all the antelope species in the Kruger National Park and have become a common sight along most game viewing routes. After only a short time, most visitors to game reserves stop paying too much attention to these herbivores. If they were less common, I am sure they would draw a great deal more attention as they are without a doubt the most interesting of the antelope species in the Greater Kruger.

They are one of the few indigenous mammal species to have increased in numbers and range over the last century. This can be attributed to a number of factors. Their generalist approach to food allows them to both graze (eat grass) and browse (eat leaves), hence their tolerance to a variety of habitats. They also have constant access to water as there are many permanent waterholes across the Kruger. Lastly, their synchronised births in a three to four week period at the start of summer a flooding of the bushveld with lots of impala lambs. Consequently, even though the predators are going to eat more than their fair share of babies during this time, there are so many around that it is impossible to eat them all. A good number will survive this most vulnerable period of their lives and will successfully make it through to adulthood.

The myth has always been that impalas can and will hold off their birthing until the first rains have fallen and as a result, we tend to only see baby impalas after the first summer rains. Sadly though, this is nothing but a myth and after six and a half months, the impala lamb is ready to come out and there is no turning around and telling it to stay in there a little longer and wait for the rain!

A more important factor affecting the slight variations in the peaks of the lambing season from year to year come about from another important part of the breeding process... and that is the all-important act of when the baby is actually made!

With the approach of autumn, days grow shorter and the diminishing of light reaching the pineal body in the impalas’ brains initiates the release of hormones, including androgen and testosterone. This all contributes to the ram’s changing behavior. The males start running around, chasing one another as well as the females and roaring the days and nights away. This physical demonstration of the hormonal changes taking place inside of the rams actually becomes the physiological trigger that causes the females to synchronise their oestrus cycles. In other words, it is the boys behaving badly that brings the females into oestrus at the same time!

So, just how badly are these boys behaving? Considering that for the most part, it is only the territorial males that get an opportunity to mate, they are prepared to put life and limb on the line to establish themselves as territory holders. Guided by hormones, they will do their damnedest to keep all the other challenging males out of potential territory as well as keep the females within the confines of his small area so that he  can mate with them!

The pressure for territories is extremely high and, as a result, even the strongest males will only hold onto a territory for a week or so before losing out to a fitter bachelor that has been waiting on the side lines for a chance.

The territorial males will approach any male that enters his territory and attempt to deter them with displays of dominance, but if that fails, they will physically engage in a tussle with their heavily ridged, rapier-sharp, lyre-shaped horns.

When tussling, the intention is no doubt to cause injury to their opponent and stab them with their horns, but despite the apparent ferocity of these engagements, very few fatalities result from these fights (possibly as a result of the thicker skin that male impalas have in the neck and shoulder region). Should the territorial male lose out to a newcomer, he will once again fall into the pool of bachelors hanging around on the outskirts of the other males’ territories.

Here, he will be less active and spend time feeding well, practicing his fighting and building up his strength to hopefully challenge once again for his territory before the end of the mating season. The new male that has taken control over the territory will now have his days filled with running around chasing other bachelors out of the area, fighting off challengers, and trying his best to keep the females within the confines of his territory until he too is worn out by this vicious cycle of hormone-driven behaviour. However, for the chance to mate and spread one’s genes, it is all worth it!

To help keep the females within his territory, a ram will constantly chase them deeper into his enclave, but he also employs some trickery when the determined females appear to be making their way into his neighbour’s patch of land. The dominant ram will pause and stare intently into the adjacent territory and begin alarm-calling, as if he has just seen a predator, hoping that this will dissuade them from walking into the danger that is not actually there!

Now the excitement not only comes in the form of watching the male impalas going through all of these antics, but also with the associated increase in predation on male impalas at this time of year. One of the challenges for a hunting leopard is finding the prey to stalk, but with the male impalas running around advertising their presence so frivolously, it makes the predator’s jobs much easier. Combined with the fact that the impala ram’s minds are focused almost entirely on one thing, it does lead to a marked increase in male impalas falling prey to leopards, and that tends to please even the most experienced safari goers!

So, next time you are on safari in April or May and you hear a roar coming out of the bushes nearby, don’t start to panic just yet, as chances are that is simply an impala looking for love!

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