2017 Mar: The Great Monkey Cascade, Geladas in the Simiens

I recorded the following for From Our Own Correspondent, the BBC programme on Radio 4. The audio can be heard here by clicking through to the time mark of 22m 20s:

High on the roof of Africa something extraordinary happens every sunset, a mass display of coordinated primate behaviour. It is in part shocking, comic and, in these straitened human times of walls, travel-bans and nationalism, rather heart-warming. It is `the great African monkey cascade’.

A leonine mane and a vegetarian diet

The setting is the summit ridge of the Simien Mountains, a thinly populated plateau in the highlands of Ethiopia, so high in fact it gets its own taxonomic treatment; welcome to the Afro-Alpine zone. It’s like nowhere else on the continent, a rolling massif where water freezes overnight and snowfalls are not uncommon. Peculiar plants thrive here like the Jurassic-looking `giant lobelia’ that flowers just the once in a 15 year life span, launching a seed-bearing phallus 20 ft up into the sky.

A stand of giant lobelias with a sprinkling of flowering phalluses

The animal population has also evolved strangely here in the Simiens. Among the lobelias pads Africa’s rarest carnivore, the Ethiopian Wolf. More `Wile E Coyote’ than `White Fang’, it has the build of a rangy fox, surviving on nothing much larger than rodents.

Ethiopian Wolf – More Wile E Coyote than White Fang

But the unique primate of the Ethiopian highlands that most human visitors encounter is the Gelada or Bleeding Heart Monkey. In truth, they are hard to miss because, unlike most other primates, they happily co-exist in huge numbers.

A mane of hair is needed against the intense nighttime cold

Grass seeds more interesting than bipedal visitors

Scientists record that chimpanzee communities have a ceiling of about 50 individuals. More than that and things begin to fall apart, violently. Not so the Gelada. They happily commune by the hundred, groups of 500 or more being quite common. And without getting too clumsily anthropomorphic, an encounter with Gelada, walking quite safely within one of their vast groups, does start one thinking.

Safe to approach

Is it because they are vegetarian that they get on so peacefully? Rarely for primates, they eat nothing but grass, grazing as closely as any goat, shuffling their bottoms along in a unique Gelada gait and picking away with fingers so dexterous they can extract grass seeds one at a time. Or perhaps it is that they are matriarchal? Not for the Gelada the chest-beating display of other primates. Here breeding mothers are key, not Alpha Males. Or is it because they are so good at communication? Research indicates the Gelada are second only to humans in their range of recognisable sounds.

As the sun dips the geladas mass by the hundred

Whatever the cause of their peaceful co-existence, the display I found most extraordinary came at twilight when I witnessed an enormous group doing something that was wonderfully non-individualistic, maximizing the chance of the biggest number making it through the night safe from leopards, hyena and other nocturnal threats; they threw themselves off the mountain.

Perilous descent to the roosting caves

High though the Simiens are, the thing that makes them truly fantastic, and which draws tourist trekkers like me, is the escarpment, a freak of tectonics that has, in effect, removed half of the mountain range. In its place are cliff walls dropping away thousands of vertical feet, and a curtain of buttressed rock that stretches along the massif’s northern flank for more than forty miles.

It is to this giddying lip that the Gelada come each evening. Just as the sun goes down and the temperature begins to plummet, they mass by the hundred and then … they jump. Mothers do it with babies clinging to their backs, adolescents do it with plenty of screeching, the old ones do it with of bit of stiff-legged awkwardness. It lasts minutes and, with so many animals involved, at peak flow it looks, in the failing light, like a furry, boisterous waterfall.

The mane of an adult gelada wafts as he tumbles

They are heading for caves to spend the night safely. The steeper the better, in terms of protection, so down they tumble on slopes way too perilous for humans. Grass tussocks give just enough cushioning to bounce on and grass fronds give just enough grip to slow the descent before it gets out of control. At first, I was convinced they were going to perish and then slowly my anxiety turned to amusement at their gambolling antics. I swear some of the younger ones pushed each other like human teenagers mucking about poolside.

The last to come were the mature adults who had set up guard on the very lip of the cliff. Eyes that all day had looked down for morsels were now swung horizontally, guarding against the stealthy approach of predators. Only when every last member of the group was safely accounted for would the guards themselves take the plunge. All for one and one for all: an old lesson perhaps but one worth remembering.

On the lookout for approaching predators

A head for heights is in the gelada genes