BIOMES OF THE EARTH - GRASSLANDS Part 7 pot

world’s most spectacular annual migration takes place. The

principal players are the wildebeest.

Throughout the rainy season the wildebeest live in herds

that are scattered across the plain. There are few rivers in the

Serengeti, and as the rainy season draws to a close the eastern

part of the plain begins to dry out and the pasture deterio￾rates. Wildebeest herds in the northeast start moving south￾ward, joining with herds from the southeast, moving west￾ward out of the Ngorongoro area. Herds of Burchell’s zebras

inhabit the same areas as the wildebeest, both species feeding

on red grass (Themeda triandra; see “Savanna grasses” on

pages 95–98). The zebras also join the wildebeest herds and

move with them. By the start of the dry season, usually in

early June, the combined herds comprise about 1.5 million

wildebeest, 300,000 Thomson’s gazelles, and 200,000 zebras,

as well as other species of antelope and some buffalo. The

herd is accompanied, of course, by lions, leopards, cheetahs,

hyenas, hunting dogs, and jackals—the predators and scav￾engers that hope to live well off this vast source of meat.

156 GRASSLANDS

The African elephant

(Loxodonta africana)

lives on the savanna in

herds, each herd led by

the oldest female, called

the “matriarch.” This

calf will continue

suckling from its mother

for three or four years

(sucking with its mouth,

not its trunk) before

advancing to an adult

diet of grass and leaves

during the rainy season

and twigs, branches,

and tree bark during the

dry season. (Courtesy

of Fogstock)

GRASSLAND ECOLOGY 157

Wildebeest

(Connochaetes

taurinus), also called

the brindled gnu, are

antelope that graze the

savanna in immense

herds. When they

migrate in search of

better pasture, up to 1.5

million of them may

travel together. These

wildebeest are crossing

the Serengeti.

(Courtesy of Mitsuaki

Iwago/Minden Pictures)

The herds spend the dry season in the moister west of the

plain, and as the dry season nears its end in about November,

they continue along their circular route, back to the northern

and eastern plains. The complete circuit is about 500 miles

(800 km) long, and many animals die along the way.

Soon after the migration begins, the wildebeest mating sea￾son commences. Each bull attempts to establish a territory it

defends against rivals and in which it can contain a herd of

females. This is possible only while the vast herd pauses in its

journey. Once the animals start moving again, the females

disperse. Consequently, mating takes place for only a few days

at a time. Nevertheless, many of the cows become pregnant

and give birth to their calves just as the rainy season is about

to begin.

The wildebeest sometimes deviate from this pattern. If the

rains are light or uncertain, they may leave earlier or later.

They may even begin the westward movement, only to

return after a few weeks. When it follows its usual course,

however, the wildebeest migration is one of the most impres￾sive sights in the world.