Herd

[citation needed] The word herd, as a noun, can also refer to one who controls, possesses and has care for such groups of animals when they are domesticated.

When an association of animals (or, by extension, people) is described as a herd, the implication is that the group tends to act together (for example, all moving in the same direction at a given time), but that this does not occur as a result of planning or coordination.

The reason why animals form herds can not always be stated easily, since the underlying mechanisms are diverse and complex.

Living in groups evolved independently multiple times in various taxa and can only occur if its benefits outweigh the costs within an evolutionary timescale.

However, animals that are weak and slower or on the periphery are preferred by predators, so that certain positions within the group are better than others (see selfish herd theory).

[4] The effect of collective vigilance in social groups has been widely studied within the framework of optimal foraging theory and animal decision making.

It could be shown in many studies (especially for birds) that with increase in group size individual animals are less attentive, while the overall vigilance suffers little (many eyes effect).

This means food intake and other activities related to fitness are optimized in terms of time allocation when animals stay in groups.

Working together significantly improves foraging efficiency, meaning the net energy gain of each individual is increased when animals are feeding collectively.

It has been shown that larger groups of lions tend to be more successful in protecting prey from hyenas than smaller ones.

In terms of Optimal foraging theory, animals always try to maximize their net energy gain when feeding, because this is positively correlated to their fitness.

If on the other hand time allocated to foraging is fixed, an animal's gain in fitness is related to the quantity and quality of resources it feeds on (Energy maximizers).

and may induce risk of predation, animals in groups may have an advantage, since their combined effort in locating and handling food will reduce time needed to forage sufficiently.

Birds flying together in a flock use aerodynamic effects to reduce energetic costs, e.g. by positioning themselves in a V-shaped formation.

Another benefit of group living occurs when climate is harsh and cold: By staying close together animals experience better thermoregulation, because their overall surface to volume ratio is reduced.

Flocks of raven are able to actively defend themselves against eagles and baboons collectively mob lions, which is impossible for individuals alone.