A bachelor herd is a gathering of (usually) juvenile male animals who are still sexually immature, or of 'harem'-forming animals who have been thrown out of their parent groups but not yet formed a new family group.

Examples include seals, dolphin

Dolphin

Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s, lion

Lion

The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...

s, and many herbivore

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

s such as deer

Deer

Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...

 and horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s. Bachelor herds are thought to provide useful protection for social animals against more established herd competition or aggressive dominant males. Males in bachelor herds are sometimes closely related to each other.

In many species, males and females move in separate groups, often coming together at mating time, or to fight for territory or mating partners. In many species it is common for males to leave or be driven from the group as they mature, and they may wander as lone animals or form a bachelor group for the time being. This arrangement may be long term and stable, or short term until they find a new group to join.