Group Defense

Group Defense
Many animals find safety in numbers by living in large groups. Bison live in herds. Tuna and many other fish species form large schools. Geese and other birds form flocks as they migrate from one place to another when the seasons change. Aphids cluster together on stems.


Living in a group helps animals defend themselves against predators in several ways. lone animals must rely only on their own senses, but an animal in a group benefits by having lots of other animals’ eyes, ears, and noses on the alert for danger. An animal in a group also has a smaller chance of being the unlucky individual picked out by a predator.

In addition, a group of animals fleeing from a predator can create confusion. This makes it harder for a predator to focus on one animal to catch. A school of fish will split in two to avoid a predator, and then quickly regroup behind it. A herd of zebras can become a dazzling display of black and white stripes, making it more difficult for a lion to see where one zebra ends and another begins. Starlings clump together when a hawk approaches. This makes it harder for the hawk to single out one bird.

Animal groups may be made up of just one species. Striped coral-reef catfish, for example, travel in a dense, ball-shaped school when they are young. Many seabirds nest in crowded colonies on islands and gang up on trespassing predators.

Animals may also form mixed groups, such as the herds of hoofed animals that migrate across Africa’s plains. There, shaggy horned animals called gnus form herds of up to one million animals. Traveling along with them are tens of thousands of zebras and gazelles.

Groups of animals also may work together to drive off a predator. One of the most famous examples of group defense is the circle formed by musk oxen. Musk oxen are huge, shaggy cattle that live on the broad, snowy lands of the Arctic known as the tundra. Females and young live in herds year-round. Males join these herds for part of the year.

If wolves attack a herd, musk oxen form a circle with their calves in the middle and their horns facing out. The wolves face a wall of horns backed up by hundreds of pounds of muscle. Musk oxen also will rush out and try to hook a wolf with their horns. Scientists have seen other animals, such as gnus and white rhinos, form defensive circles.

Zebras do not form circles, but small herds do work together to foil predators. If a pack of hyenas creeps up on a herd, a male zebra charges at them, ready to bite and kick. The females and young gather together and move away. Often a female known as the lead mare guides them. Wild horses also behave in this way. Other animals, such as elephants and cattle, approach and threaten predators that come near their herds.

Large African monkeys called baboons also live in groups. They sometimes work together to drive off predators. Scientists have seen males of one species of baboon ganging up on leopards and dogs to chase them away. A smaller monkey, the red colobus, also teams up with other males to defend their group when chimpanzees attack. The male monkeys get between the females and their young and the chimps. They leap onto the chimps and bite them.

Many species of small, burrowing mammals cooperate against predators, too. These animals alert each other to danger. Meerkats are weasel-like animals that live in dry lands of southern Africa. When they leave their burrows to look for food, a few animals stand guard. The guards climb onto a rock or a termite mound and stand on their hind legs. They scan the skies for eagles and hawks. They also keep an eye out for hungry jackals. If a predator appears, the guards call quickly and sharply. This is the signal for everybody to dive into the burrows.

North American prairie dogs, which are related to squirrels, also live in burrows. The burrows cover a huge area of land known as a prairie-dog town. Prairie dogs do not post guards. Yet, because there are so many prairie dogs, someone in the town is likely to spot a hawk or a coyote. Prairie dogs that spot danger will give a danger call. At this signal, everybody scurries underground to safety.