A history of migrating herds
Huge herds of migrating animals are an amazing sight.
In 1871, one herd covering 3,200 km2 (1,250 square miles) was seen crossing the Arkansas River. That’s more than twice the size of London! But people soon put paid to this magnificent spectacle by killing bison.
Between 1870 and 1875 alone, more than 12.5 million bison were shot, and by 1889 only about 1,000 were left. Today, thanks to conservation, there are about 500,000 – all within national parks.
A similar slaughter took place in South Africa during the 19th century, where herds of migrating springbok were far bigger than anything seen in Africa today. In 1896, one herd, measuring 125 km (77 miles) in length, took two weeks to pass by. These huge herds did such damage to crops that the government instructed farmers to shoot springbok on sight. Today this graceful antelope is only common on nature reserves.
Caribou migration across the tundra
In spring, as the snow starts to melt, the pregnant caribou cows lead the long march north. They’re in a hurry to give birth. After two months, they reach the Arctic coast of Alaska, where they find plentiful lichens, few predators and a cool breeze that keeps insects at bay.
The calves are born in early June. By July, the insects are worse and food is running low. Tens of thousands of caribou spread out across the landscape to find food and escape the biting bugs. As the first snows start to fall, they gather into huge herds and start heading south – followed by bears, wolves and other hungry predators.
By November, the caribou reach the forests where they spend winter. Among the trees the snow is not so heavy – and it stays soft, so they can dig down to feed on lichens.
The temperature can fall as low as -50°C. But the caribou are tough, and special hollow insulating hairs on their coats help them stay warm enough to survive. They spend winter feeding and gaining weight, ready for the spring journey back north.
Migration in the Serengeti
On East Africa’s rolling Serengeti plains, more than one million grazers gather each year for the biggest movement of large animals on Earth. Blue wildebeest, which are a species of antelope, make up the biggest numbers. Other animals include zebras and gazelles. Each species grazes a different part of the grass, but they all depend upon rain for the grass to grow.
During the rainy season, from December to March, the wildebeest herds stay in the south, where the lush grass allows them to fatten up and have their young. As the rains dry up and the grass starts to disappear, they migrate north.
Young wildebeest can walk within an hour of being born, so they can keep up with the herd as soon as it moves. This is just as well, since lions, hyenas and many other predators lie in wait. On the way they have to cross the treacherous Mara River, where thousands drown or are grabbed by crocodiles.
The wildebeest reach their northern feeding grounds around June, where they mate and enjoy the lush new grasses for a few months. But soon, the rains are falling again in the south, and the wildebeest are restless to return. By December, they are back on their southern breeding grounds, preparing to give birth to next year’s calves.