Many different animals exist together in groups for a variety of reasons. Groups may be temporary (such as a flock of migratory birds or a congregation at a water hole) or permanent (such as a baboon family troop). The complexity of the group organisation dictates the need for structure and communication within the group to ensure the survival of the group. Especially amongst social insects (e.g. bees) and mammals, different individuals may have different roles depending on age, sex, or status; each contributing to the overall survival of the group.

Protection
Flocks of birds, schools of fish and herds of grassland animals will "close ranks" when threatened by a predator .This may confuse predators or make the group appear like an animal too large for the predator to attack. The more vulnerable breeding females and young are often kept in the centre with the stronger males defending the periphery. The group might also collectively swoop and drive away the predator.

Penguins in Antarctica "huddle" to conserve body heat. They constantly re-group as the ones on the edge become too cold.

Moving flocks often "take turns" at being the leader which is the most tiring position due to frictional drag. A similar tactic is used by humans in teams of racing cyclists!

Food gathering
By hunting in packs, wolves and wild dogs can capture prey too large for any individual to catch. This provides food for the whole pack, including the less agile breeding females and young. Other individuals acting as sentries can alert them of impending danger.

Many animals (e.g. bees) individually locate food sources and then communicate to the group to maximise food gathering.

Pelicans often swim together along a lake when feeding, so if a fish escapes one bill, it is likely to swim into another!

Reproduction
Many species (e.g. gulls) flock together during the breeding season to form a colony. This is partly because of specific needs (such as nesting sites) but also for protection.

In animals which need considerable parenting, involving both physical protection and learned behaviour, groups provide this support and influence. This is seen especially in baboon troops, and extended human families. This also allows the teaching of parenting skills to older siblings.

Among mammals such as deer, antelopes and sea lions, the group consists of a harem containing just one adult male, several females and their young. The other males live separately and only interact at breeding time to test the dominant male for the right to breed. This helps group stability.

Group cohesion
Keeping the group together is helped by specific calls (e.g. bats), leaders (lead cattle will herd the others), and social interactions such as dominance hierarchies. Acceptance of dominance by other group members (such as pecking order of chickens) reduces competition for food and mates without fighting and so conserves energy.

Social insects
Social life in the insect world is advantageous to individuals, providing co-operative defence and efficient division of labour.

Bee hives have a breeding queen, male drones for mating with the queen, and female workers which carry out all activities inside and outside the hive.

In a termite colony, most of the termites are workers which care for the young and gather food. Soldier termites guard the nest. The king and queen termites are sealed inside the royal chamber where they live and mate for longer than 20 years!