In the previous month’s journal we welcomed the arrival of the migrating herds, as well as noted the passing overhead of millions of globe skimmer dragonflies. In keeping with the theme of migration, I wanted to try and unlock why, with all the same opportunities, resources and challenges, the wildebeest dominate in numbers that no other ungulate can match.
The years of research spent observing, studying, noting, sampling, interpreting and hypothesizing by a gentleman called Dr Richard Estes gives some interesting insight into understanding the “clock” that sets the rhythm of the Serengeti Migration—the wildebeest breeding cycle.
The synchronization of the females calving is unparalleled among African mammals. Around February every year approximately 1.5 million wildebeest, gather in the southern open plains of the Serengeti ecosystem. There, amid the green flush of the short-grass plains, females give birth to some 500,000 calves and about half of them are born within a two-week window. The sheer number of calves overwhelm the predator population and I feel confident that we would all agree that this is certainly a winning tactic to use to your species advantage.
What’s often over looked and not considered is how half a million calves can be conceived in such a short space of time to ensure that as many as 90% are born within two weeks of each other. This is only made possible by an equally amazing trick eight months earlier, when hundreds of thousands of wildebeest cows strung out over hundreds of square miles come into oestrus within an equally short period.
How do the wildebeest move so closely to the same beat that proves so successful to their populations’ dominance out here while the zebra, gazelles, elephant, buffalo, giraffe, eland, lion and hyena just can’t keep up? Estes believes that the answer lies in the May-June rutting season which he notes as “one of the greatest mammalian events.” Over the months of May and June when we head out into the bush we hear the herds long before we see them; and when we do find them, we find the herds overseen by territorial bulls, actively patrolling with their heads held high, frequently in a rocking canter and often crashing to their knees to lock horns with other bulls that do not beat a hasty retreat. Each bull is trying to hold an attractive piece of Serengeti real estate to encourage cows to remain longer until they are either ready to mate or, if in oestrous, to stay for multiple copulations.
Two wildebeest bulls locked in battle… until the bitter end.
Ones sense of hearing is overwhelmed when you spend time around the herds, due to the bulls’ consistent deep, guttural grunting and bellowing. The cumulative effect rumbles, “…like waves against a headland,” says Estes, creating perhaps the loudest noise of any assemblage of antelope in the world. Estes suggests that maybe this “noise” plays a key role in solving the mystery of the females’ precisely synchronized oestrus cycles that ultimately leads to their success in terms of numbers.
Estes’ research saw three small herds of captured wildebeest females isolated in 25-acre enclosures. One group was exposed to three weeks of recorded rutting calls. Another group heard the same calls with the added stimulation of a live, but quiet, bull. The control group heard no bulls, saw no bulls and smelt no bulls. The research suggested that even if the females couldn’t see a bull, the recorded rutting calls affected the cows who in turn showed more activity, sniffing each other and became more aggressive. Cows appeared to react more strongly to the audio of a dominant bull over the noise of the herds and hormone levels in the residues of faecal samples seemed to indicate a shift towards oestrus.
The research and observations continue today and there is still no definitive answer, but what it does do is make us stop and appreciate for a moment, that the crescendo of noise these bulls make day and night during the rut, shouldn’t be overlooked and just maybe is one of the fundamental keys to understanding the ins and outs of the success of the Great Migration.