It’s Baby Season
In the November and December months, so much new life surrounds us at Sabi Sabi. The leaves have begun to sprout on all our deciduous plants, the fresh grass shoots are emerging, and the little wildflowers are adding a splash of colour to an environment that was dominated by dull browns and grey, and we are also seeing new life appearing amongst the seasonal breeders of the animal kingdom. That is why we affectionately call this Baby Season, writes ranger Amy-Leigh Roberts.
With the first summer rains, the termite alates take to the skies in their thousands, with the purpose of finding a mate and starting a new colony, and nearby, baby birds are trying their wings at flying under their mothers’ watchful eye as they fledge their nests. Then, as if by clockwork, after those first rains, the first baby Impala is sighted… and then another, and another, and another, until we are seemingly overrun by these adorable, spindly-legged little creatures.
In fact, the timing of these new arrivals is so perfectly on point each year that it is believed that Impala ewes were actually able to hold off from giving birth until the first rains arrived, however, this is not actually the case. As with any mammal, when the baby is at full term and ready to appear, no force can stop it, but the question remains how all the females get it right each year. Well, this comes down to the biology of the animal, and it starts a good 200 days prior.
The Season for Mating
As the seasons begin to change from summer to winter around March/April, the days become shorter, the intensity of light changes, and the temperatures – which can reach high 30s to low 40s (°C) – begin to drop as we approach the colder, drier months of the year. The grasses begin to die out and the trees begin to lose their leaves. The changing environmental conditions and variations of the nutritional value of the vegetation stimulate changes in the hormone production of the Impala.
Testosterone levels in males increase, leading to gonadal growth and increased aggressive and territorial behaviour, while the females also experience this hormonal change as their bodies prepare for estrus, the period in their sexual cycle during when they are in heat and ready to mate.
The males not only scent-mark more regularly – using secretions from sebaceous glands on the forehead that they deposit on vegetation by rubbing their faces and horns vigorously on vegetation – but they also regularly produce a call (likened to a roar), which is made up of a combination of explosive snorts and deep guttural grunts. Where most of the year is spent with males and females associating freely in mixed herds, and males being tolerant of each other, there is a definite increase in territorial behaviour. The presence of other males of breeding potential is not tolerated in the area where a male begins to establish his territories.
This results in a clear division of the sexes, with breeding herds of females accompanied by a single dominant male, often referred to as harems, and herds of young and sub-dominant males, often referred to as bachelor herds. And so, begins the process of the rutting season.
Rules of the Harem
Yearling males, which are now sexually mature, but still far too small and inexperienced to win any fight for dominance, are chased out of their mothers’ herds, because even these young males have been seen to attempt to breed when the dominant male is preoccupied. They will often seek the comfort and safety of the rest of the boys who have been displaced, forming herds in which they are able to spar and develop the skills to one day win the role of harem male.
Other mature males – those who are 4 years and over – are also not tolerated in the vicinity of a more dominant male’s territory, although there is the greater possibility of seeing these males roaming an area alone, as a way of increasing their competitive advantage. The fewer other males around him, the fewer contenders there are competing for the role of harem male, and the time is spent ensuring he is strong, well-kept and in good physical condition to win that next fight.
What these males rely on is the fact that while a harem male has the right to breed with the females that come into estrus when he is dominant within the harem, he also has the immense responsibility of protecting his position. This includes the constant ‘roaring’ and snorting calls, which announce to both the females as well as potential competitors, that he is strong and worthy. He regularly must fight off challengers for his position or chase off young males who hope to steal an opportunity for breeding with a female he is not focused on. The male is constantly herding all his darling females to keep them nice and close where he can keep a close watch over them.
A Fleeting Role
And while all that is going on, he must try to determine which females are receptive and ready to mate, and he must take the time to court them… He really does have his work cut out for him! So, it is no wonder that within 8 to 10 days his reign as harem male comes to a sudden end, as his body condition deteriorates to the point where he no longer wins each fight, and a challenger takes his throne.
In this way, Mother Nature very cleverly ensures that over the peak rut, which lasts between three to four weeks, a number of different males have the potential to sire young, and so introduce genetic variation into the offspring that will arrive approximately 6 months later. She has also considered the fact that lactating mothers and developing youngsters need the best quality food for maintaining condition, and so the gestation period brings us to the opposite side of the spectrum from the rut.
As the days grow longer and hotter, the light from the sun seems to intensify and the first drops of rain fall on the parched earth, giving new life to the vegetation. Once again, we see the changing environmental conditions and variations of the nutritional value of the vegetation, and the perfectly timed arrival of the new kids on the block.
Lambs Enter the Story
When a female is ready to give birth, she leaves the safety of the herd and isolates herself in the hope that the absence of other individuals might prevent the attention of a predator finding her in this vulnerable time. Usually around midday, when the predators are least likely to be active, she will produce a single lamb, which she will groom to remove the strong odour of birth, and then leave concealed for two to three days, until it is strong enough to keep up with the herd. She will only visit the lamb a few times during the day for grooming and nursing, to avoid attracting attention to the hiding place.
Her lamb will then join the rest of the lambs in a creche, where they spend all their time playing, grooming and resting together unless they are being nursed by their mothers. These large creches are important, not only for learning and development but also for ensuring the survival of at least 50% of the offspring from that season. This synchronised breeding – where all the young are produced at the same time – is a survival technique for the species. By having so many young together means that although many fall prey to the array of predators taking advantage of them as a resource, from the felines (Cheetah, Leopard and Caracal), canines (African Wild Dogs and Jackal) to large eagles (Martial Eagles) and even reptiles (Crocodiles and Pythons), it is impossible that an entire next generation would be removed, as there are simply too many.
The lambs also develop very quickly. By four and a half months, they are weaned and able to live independently of their mothers, although they will remain within the safety of their natal herd (the herd into which they are born) for about a year, until the yearling males will be pushed out. However, the yearling females remain in the herd until they, too, are ready to conceive, usually after two years, depending on body condition.
Constant Circle of Life
And thus, the cycle continues, ensuring Impala remain one of the most common antelope species to see at Sabi Sabi, and as much as they become just another Impala around the corner, you have to give credit where credit is due… this species is strong and adaptable, and deserves recognition for thriving in this often harsh environment.