Capybaras are social animals, usually living in family groups composed adult males, adult females, and young. Mean group size is six animals, but they exhibit variation in size during the year. In the pantanal, for example, the group size increases from the beginning of the year (rainy season) to the middle of the year (dry season). Groups of eight to 12 animals are relatively common.

The group composition is usually formed by a dominant full adult male, one or two full adult submissive males, two to four or more adult females, and the others are subadults and young. The dominant male in the group exhibits aggressive and hostile behavior to keep the other males submissive. Females in the group also display a hierarchy. The social behavior reflects group sizes. They are docile, quiet, crepuscular animals but may show activities during the day, except for some rest periods in their shelters in the forest, during the hotter hours of the day.

Ranging behavior is variable. The home range occupied by a given social group averages 200 acres (80 ha), but may be much larger in some cases, depending on the season of the year. This home range contains foraging area, patch of woodland or forest where the group rests and reproduces, and water where the animals swim. Neighboring groups may share parts of their home ranges, but maintain some core areas within these home ranges that are for the exclusive use of the group. In flooded areas, groups have larger ranges and core areas during the dry season than during the rainy and flooding season, a change that is associated with the reduction of

A capybara (Hydrochaeris hydrochaeris) with a bird sitting on its back in Pantanal, Brazil. (Photo by Animals Animals ©Fabio Colombini. Reproduced by permission.)
A capybara (Hydrochaeris hydrochaeris) mother, followed by her young. (Photo by Erwin and Peggy Bauer. Bruce Coleman, Inc. Reproduced by permission.)

the feeding grassland habitat. During the dry season, larger groups are seeing feeding on the grassland seasonal fields. During the flooding season, the groups split into smaller groups, and disperse among the patches of the forest or woodland, using more of the water habitats of ponds or inundated areas.

Capybara groups in the wild have been observed displaying three different activities: foraging on grasses, sleeping or resting, and exhibiting social interactions. They display distinctive postures, movements, sounds, and activity patterns:

• Alert. The capybara remains immobile on its four feet or sitting, staying in whatever position it happens to be in at the time of the stimulus. The animal keeps its head raised, looking in one direction, with the ears erect. If an intruder continues to approach, the capybara barks like a dog, jumping into the water or running away.

• Grazing. The capybara grazes, moving slowly while foraging, sometimes raising its head to check its surroundings.

• Lying. Usually the animal lies down with its head erect while resting.

• Sleeping. The animal sleeps intermittently during the daylight hours and evening in wooded areas.

• Sitting. This is also a resting posture, common on the river banks.

• Swimming. Capybaras are good swimmers and divers.

• Intimidating. One dominant male or female circles an intruder or submissive capybara in order to impose its dominance or to ward off an approach.

• Fighting. Two animals in an upright position embrace each other and engage in a fight or a male and female exhibit courtship.

• Contacting. During the encounter between two animals one may actively initiate contact, either sexual or antagonistic. The male may inspect the sexual receptivity of a female by nasal-genital contact.

• Mounting. The female swims back and forth in the water, pursued by the male, and when she displays a receptive position, the male mounts.

• Maternal care. Involves nursing with a mother and her young.

A capybara (Hydrochaeris hydrochaeris) with young in the floodplain of Brazil. (Photo by Harald Schütz. Reproduced by permission.)

• Marking. The male rubs his snout gland up and down a stalk, or the animal straddles a stalk in order to rub it with its anal scent gland.

Male to male aggressive interaction is the most common display seen in the field. Subadults of either sex are always subordinate to adults of either sex. The dominant male of the group initiates the attack. Some subadults suffering attacks are excluded from the group and become satellite animals. These animals suffer stress and are subject to being weak, sick, and killed by predators.

The males compete more strongly for access to breeding partners than do females; a female's reproductive success depends on her ability to acquire food. The females spend a great deal of their time caring for young of different ages, who move from one female to another. The females suckle young in a creche-behavior fashion.

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