The largest gatherings in the animal world

Around the world, large gatherings of animals occur due to the need to escape, feed or reproduce, playing a key role in the survival of species.

Terrestrial mammals

Wildebeest and zebra cross a river during their migration. (Photo: Gudkov Andrey).

One of the largest animal migrations by weight occurs across the Serengeti each year, when over 2 million wildebeests travel in search of green grass during the rainy season. This great migration is one of the largest wildlife events in Africa and is vital for the wildebeests to feed and keep their young alive. This is not easy, as prides of lions and hyenas prowl the area. Their pursuit of food is joined by other herbivores such as antelope and zebra. However, as they run across the grasslands and cross rivers, they attract more and more predators such as crocodiles.

This may be one of the heaviest gatherings of animals on the planet, but it's not the biggest. Among mammals, that title belongs to the cave-dwelling free-tailed bat Tadarida brasiliensis, which lives in colonies of up to 15 million. These migratory animals spend the winter in caves, but come February, they head to Texas and form large colonies to raise their young.

In the air

The red-billed ibis moves like a long cloud. (Photo: Saffa Capture).

Red-billed aardvarks fly in flocks of several million, moving through the bush in a noisy cloud in search of food. The birds are closely studied because they can damage agriculture and threaten food security in some areas. They exist in huge flocks that can take hours to fly overhead. They are the most abundant bird on Earth, with an estimated population of 1.5 billion.

Under the ocean

Mollusks are a food source for some of the largest animals on the planet. (Photo: Andrea Izzotti).

From October to November, red crabs ( Gecarcoidea natalis ) emerge from their jungle burrows. 50 million crabs will crawl across Christmas Island, where special crab highways and bridges have been built to help them avoid traffic. There are about 100 crabs per square meter on egg-laying night, when female crabs gather on the beach, ready to release their clutches.

Farther offshore, the most abundant are krill, tiny crustaceans that provide food for some of the planet's largest animals, such as humpback and minke whales. Krill can form massive schools in the Southern Ocean, stretching up to 20 kilometers and containing more than a million tons at densities of more than 10,000 individuals per cubic meter, the largest density of any animal in the world, according to the Antarctic Fund.