National Geographic - USA (2021-12)

taken the podium to announce

astonishing news: He and another

ecologist, Mike Norton-Griffiths,

had counted the largest ungulate

herd ever recorded.

The feat of accurately calculating

the size of such a large migratory

herd—before the use of satellites

and other advanced technology—

was impressive enough, but even

more stunning was that this herd

was the Serengeti’s wildebeest

population.

Beginning in the 1890s, the

wildebeest had been decimated

by outbreaks of a virus known as

rinderpest, which is related to the

measles virus. Though it’s harmless

to humans, rinderpest is lethal to

domestic cattle and their wild cous-

ins, including the African buffalo

and wildebeest.

An effective vaccine had been

widely administered by the early

1960s, stopping the outbreaks

among cattle, and the wildebeest

was rebounding with astounding

speed. Before the vaccine largely

wiped out rinderpest, the Seren-

geti’s wildebeest population was

roughly 260,000. But in just 17

years, from 1961 to 1977, it had more

than quintupled, to 1.4 million. Sin-

clair showed me a black-and-white

photo he’d taken during one of his

counting flights. A massive herd of

wildebeests covers the land from

horizon to horizon.

But in Pretoria, his fellow scien-

tists didn’t share his enthusiasm.

“What I got was people standing

up saying, ‘This is the most irre-

sponsible thing I’ve ever heard,’ ”

he recounted when we chatted over

Zoom. “ ‘What we should be doing

is killing half the population.’ ”

That was the prevailing dogma

held by many scientists in Africa

but also in places such as Yel-

lowstone, he said. They believed

wildlife populations needed to be

manipulated to stay in balance.

“They had to be controlled,” he

Increase

Decrease

Other herbivores

Predators

Grass

1961 1977

260,000

1.4 million

A POPULATION SURGE

The number of wildebeests in the

Serengeti grew fivefold in less than two

decades once rinderpest, a virus passed

from domestic cattle to wildlife, was

largely eradicated in the early 1960s.

SHAPING THE SERENGETI

The sudden population uptick set off a tor-

rent of far-reaching impacts, giving scientists

a rare opportunity to study the vital role

wildebeests play in the ecosystem.

More wildebeests eat more grass

and boost predator populations.

Less grass means less fuel

for fires. Trees regener-

ate more easily, a boon

for many species.

Grasshoppers and

Thomson’s gazelles

have less food

available to them.

DIANA MARQUES, NGM STAFF. LAWSON PARKER

SOURCES: ANTHONY R.E. SINCLAIR, BIODIVERSITY RESEARCH CENTER,

Shorter grass lets

more light and

nutrients reach

lower plants.