herd

A herd is a large social group of the same species that lives and moves together. The term is used across wildlife biology and animal husbandry to describe many herbivorous and some omnivorous species. In wildlife, herds may range from a few individuals to hundreds, and their size and composition can vary with season, resources, and predation pressure.

Herds show varying organization. In elephants, herds are matriarchal, led by an elder female; cattle and sheep often form stable, multi-age groups; deer and antelope may migrate in large, fluid bands; horses form herds directed by a dominant stallion or a breeding group. In some species, males leave the female group to form bachelor herds.

The main advantages are predator avoidance through shared vigilance (many eyes), dilution of risk, and improved foraging or migratory navigation. Herds can improve detection of food and water sources but also increase competition for limited resources and facilitate the spread of contagious diseases.

In agriculture, a herd refers to domesticated animals kept together for breeding, milking, or meat. Herd management involves breeding plans, grazing rotation, veterinary care, and protection against predators; herding dogs and fences are commonly used.

The term also appears in human contexts. In social science, herd behavior describes the tendency of people to conform to group norms, and in epidemiology, herd immunity refers to the protective effect when a large portion of the population is immune to a disease.