Wild rhythm

The Serengeti and the Wildebeest belong together. Add up all the lions, elephants, warthogs, giraffes, gazelles, zebras, impalas, topis and hyenas that live on these plains and they fail to outnumber the gnus. With their teeth, hooves, horns and dung, Wildebeest have literally cultivated the grasslands. But it's the elephants, lions and other charismatic mammals that get coffee-table books written about them. Wildebeest couldn't even get a speaking part in The Lion King.

Richard Estes speaks for them. "They are my constituency," he says. He chose Wildebeest because they were "the most interesting" of all the mammals he considered studying, due mainly to the "extraordinary performance" of the rut and the birth season's "incredible spectacle". Today, most of the world's knowledge of Wildebeest behaviour is based on the observations of 'the guru' of gnus, as Estes is known.

One of the crowd

Estes shares with his 'constituents' a determination to plod on against adversity, as well as a white beard. But Estes is willing to move against the herd. He plans to devote the next few years to writing the definitive tome on these bovids. "The Wildebeest deserves its own book," he explains, "and if I don't write it, no one will."

We are sitting on top of a granite kopje with a 360� view of Wildebeest stretching out on an emerald carpet until they fade into pinpricks on the horizon - perhaps 100,000 animals in total. A pattern of black on green is formed by the clusters of Wildebeest, each made up of 5 to 50 cows and calves, resting or grazing. Every small herd is overseen by a territorial bull, patrolling continuously with his head held high, frequently in a rocking canter. For the duration of the rut, territorial bulls within smelling distance of cows will barely pause long enough to munch a mouthful of grass. They chase young males out of their domain and herd the cows in. They remain constantly on guard to repel cow-rustling rivals, often in violent, head-to-head combat.

Crash, bang, wallop

"Just watch those two," alerts Estes. "They're going to bash heads." On cue, two Wildebeest bulls accelerate head on, hunker down on their knees and clash. The impact splits the air.

When no neighbour is available for sparring, males will attack the ground. Some become so worked up they froth at the mouth. "It's total mayhem," says Estes with delight. "The rut is one of the greatest mammalian events." Caribou bulls may fight extended battles in the Arctic, Mongolian gazelles may be greater in number, but neither can compete with this for the title of Greatest Mating Show on Earth.

The big hum

Richard Estes points his Land Rover north as the sound of the western Serengeti reverberates faintly in the distant hills. It is "the big hum," as Estes describes it, a basso profundo mating chorus of what sounds like a hybrid between a cow and a giant bullfrog.

The bulls' breeding motto is "location, location, location." They must hold a sufficiently attractive piece of land to encourage cows to linger until they are ready to mate or stay for multiple copulations if they are already in oestrus.

Pulling power

Estes divides bulls into five territorial types. The Midnight Cowboys stake their claim on the shortest grass. "They look silly with nothing to eat," muses Estes, "but at night [when predators prowl in the long grass], they get all the girls." The Made in the Shade bulls stand guard under acacia trees to lure cows out of the midday sun. The Spoilers just run through other territories, trying to break up herds and steal cows. The Go-getters work a migrating column by sprinting to the front and occupying a plot of grass where a succession of cows will pass. When the tail end of the column has passed, they race to the front to begin again. Then there are the Retards, who "set up territories where there is nothing but bachelor males and stay there maybe a week after the migration has gone," Estes quips.

Throughout this display, the air pulsates with the guttural grunting of the bulls. The cumulative effect rumbles "like waves against a headland," in Estes's words, creating probably the loudest noise of any assemblage of antelope in the world.

Rhythm method

For four decades, Estes has been pondering the mystery of the clock that sets the rhythm of the Serengeti - the Wildebeest breeding cycle. Every February, give or take a couple of weeks, more than a million Wildebeest, or gnus, gather in the south-eastern quadrant of their quasi-circular migration route. There, amid the green flush of the short-grass plains, they give birth to 500,000 calves, about half of them within a two-week window. The baby boom overwhelms the local carnivores, which, lacking refrigeration, can eat their fill and no more.

Such synchronicity, unparalleled among African mammals, is made possible by an equally amazing trick eight months before, when several hundred thousand Wildebeest cows strung out over hundreds of square kilometres come into oestrus within a short period. How do they all move to the same beat? Does the moon make them swoon, an idea advanced by some observers? Is it the love hum of rutting bulls, the theory put forward by Estes 40 years ago? Or some other force? Estes has enlisted scientists, the latest advances in molecular chemistry and 16 Wildebeest cows in an effort to reveal what makes their biological timepieces tick.

Unravelling the mighty rut

When Estes first saw the rut in 1964, he developed his theory that the 'big hum' brings on an epidemic of oestrus. "The calling of the bulls was so conspicuous," he says, "there had to be a reason." Forty years later, Estes is working with Smithsonian's National Zoological Park to test his theory.

On a reserve on the western fringe of the Serengeti, three small herds of Wildebeest females have been isolated in 10-hectare 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 bull, saw no bull, smelled no bull.

Gnu findings

Allison Moss is the PhD student running the Smithsonian's project. "There are segments of that CD that the cows really like, the part where they can hear just one male," she notes. "There are a couple of females who always get moony when they hear that."

To confirm this anecdotal evidence, researchers in Smithsonian Institution's Conservation and Research Center in Virginia are analysing hormone residues in faecal samples to detect when cows go into oestrus. The team collect samples from all the cows' droppings. Inside a makeshift lab-in-a-tent, Moss freezes, thaws, measures, boils, centrifuges and dissolves dung in preparation for a flight to Virginia, where hormone levels are measured using radioactive isotopes, a technique pioneered by Steven Monfort. It's not as simple as looking for a blue stripe on an ovulation predictor kit but safer than sticking a needle into a Wildebeest.

Endless journey

Moss is frequently up in the middle of the night coping with leopards and other project crises. She thinks nothing of spending a 12-hour day in an incredibly hot, fly-infested canvas lab. Still, she marvels at Estes's youthful enthusiasm. "The man is 76-years old, he's been doing this for 40 years, and he still wakes me up at 5.30am to look at Wildebeest with him when we're out in the field. Not because he wants the fame or he wants to publish more, he's just constantly fascinated by them."

Like the endless journey of Wildebeest, Estes's quest to understand the workings of the wild never stops.