The capybara (Hydrochoerus hydrochaeris) is the largest rodent in the world, followed by the beaver, porcupine, and mara. Its closest relatives are agouti, chinchillas, coypu, and guinea pigs. Native to South America, the capybara inhabits savannas and dense forests and lives near bodies of water. It is a highly social species and can be found in groups as large as 100 individuals, but usually lives in groups of 10–20 individuals. The capybara is not a threatened species, though it is hunted for its meat and hide and also for a grease from its thick fatty skin which is used in the pharmaceutical trade.
Its common name is derived from Tupi ka'apiûara, a complex agglutination of kaá (leaf) + píi (slender) + ú (eat) + ara (a suffix for agent nouns), meaning "one who eats slender leaves", or "grass-eater". The scientific name, both hydrochoerus and hydrochaeris, comes from Greek ὕδωρ (hydor = water) + χοίρος (choiros = pig, hog).
Classification and phylogeny 
The capybara and the lesser capybara belong to the subfamily Hydrochoerinae along with the rock cavies. The living capybaras and their extinct relatives were previously classified in their own family Hydrochoeridae. Since 2002, molecular phylogenetic studies have recognized a close relationship between Hydrochoerus and Kerodon supporting placement of both genera in a subfamily of Caviidae. Paleontological classifications have yet to incorporate this new taxonomy and continue to use Hydrochoeridae for all capybaras, while using Hydrochoerinae for the living genus and its closest fossil relatives, such as Neochoerus. The taxonomy of fossil hydrochoerines is also in a state of flux. In recent years, the diversity of fossil hydrochoerines has been substantially reduced. This is largely due to the recognition that capybara molar teeth show strong variation in shape over the life of an individual. In one instance, material once referred to four genera and seven species on the basis of differences in molar shape is now thought to represent differently aged individuals of a single species, Cardiatherium paranense.
The capybara has a heavy, barrel-shaped body and short head, with reddish-brown fur on the upper part of its body that turns yellowish-brown underneath. Its sweat glands can be found in the surface of the hairy portions of its skin, an unusual trait among rodents. The animal lacks underhair, and guard hair differs little from overhair. Adult capybaras grow to 107 to 134 cm (3.51 to 4.40 ft) in length, stand 50 to 64 cm (20 to 25 in) tall at the withers, and typically weigh 35 to 66 kg (77 to 150 lb), with an average in the Venezuelan llanos of 48.9 kg (108 lb). The top recorded weights are 91 kg (200 lb) for a wild female from Brazil and 73.5 kg (162 lb) for a wild male from Uruguay. The dental formula is 220.127.116.11. Capybaras have slightly webbed feet and vestigial tails. Their back legs are slightly longer than their front legs; they have three toes on their rear feet and four toes on their front feet. Their muzzles are blunt with eyes, nostrils, and ears on top of their heads. Females are slightly heavier than males.
Capybaras are semi-aquatic mammals found throughout almost all countries of South America (except Chile) in densely forested areas near bodies of water, such as lakes, rivers, swamps, ponds, and marshes, as well as flooded savannah and along rivers in tropical forest. Capybara have flourished in cattle ranches. They roam in home ranges averaging 10 hectares (25 acres) in high-density populations.
Many escapees from captivity can also be found in similar watery habitats around the world. Sightings are fairly common in Florida, although a breeding population has not yet been confirmed. In 2011, one was spotted in the central coast of California.
Diet and predation 
Capybaras are herbivores, grazing mainly on grasses and aquatic plants, as well as fruit and tree bark. They are very selective feeders and will feed on the leaves of one species and disregard other species surrounding it. They eat a greater variety of plants during the dry season, as fewer plants are available. While they eat grass during the wet season, they have to switch to more abundant reeds during the dry season. Plants that capybaras eat during the summer lose their nutritional value in the winter and therefore are not consumed at that time. The capybara's jaw hinge is not perpendicular and they thus chew food by grinding back-and-forth rather than side-to-side. Capybaras are coprophagous, meaning they eat their own feces as a source of bacterial gut flora, to help digest the cellulose in the grass that forms their normal diet, and to extract the maximum protein and vitamins from their food. They may also regurgitate food to masticate again, similar to cud-chewing by a cow. Like other rodents, the front teeth of capybaras grow continually to compensate for the constant wear from eating grasses; their cheek teeth also grow continuously.
Like its cousin the guinea pig, the capybara does not have the capacity to synthesize vitamin C, and capybaras not supplemented with vitamin C in captivity have been reported to develop gum disease as a sign of scurvy.
They can have a life span of 8–10 years in the wild, but live less than four years on average, as they are "a favourite food of jaguar, puma, ocelot, eagle and caiman". The capybara is also the preferred prey of the anaconda.
Natural history 
Capybaras are very gregarious. While they do sometimes live solitarily, they are more commonly found in groups that average 10–20 individuals, with two to four adult males, four to seven adult females and the rest juveniles. Capybara groups can consist of as many as 50 or 100 individuals during the dry season, when the animals gather around available water sources. Males are organized in stable, linear hierarchies. The dominant male in each group is significantly heavier than any of the subordinates, but among subordinates, status is not correlated with weight. The dominant male is positioned in the center of the group while subordinates are on the periphery. These hierarchies are established early in life among the young with play fights and mock copulations. The most dominant males have access to the best resources. Capybaras are very vocal and, when in groups, chatter with each other to establish social bonds, dominance or general group census. They can make dog-like barks when threatened or when females are herding young. Capybaras have two different scent glands; a morillo, located on the snout, and an anal gland. Both sexes have these glands, but males have much larger morillos and their anal pockets can open more easily. The anal glands of males are also lined with detachable hairs. A crystalline form of scent secretion is coated on these hairs and are released when in contact with objects like plants. These hairs have a longer-lasting scent mark and are tasted by other capybaras. A capybara marks by rubbing its morillo on an object or by walking over a scrub and marking with its anal gland. A capybara can spread its scent further by urinating. However, females usually mark without urinating and mark less frequently than males overall. Females mark more often during the wet season when they are in estrus. In addition to objects, males will also mark females.
When in estrus, the female's scent changes subtly and nearby males begin pursuit. In addition, a female will alert males she is in estrus by whistling though her nose. During mating, the female has the advantage and mating choice. Capybaras mate only in water, and if a female does not want to mate with a certain male, she will either submerge or leave the water. Dominant males are highly protective of the females, but they usually cannot prevent all the subordinates from copulating. The larger the group, the harder it is for the male to watch all the females. Dominant males secure significantly more matings than each subordinate, but subordinate males, as a class, are responsible for more matings than each dominant male. The lifespan of the capybara's sperm is longer than that of other rodents.
Capybara gestation is 130–150 days, and usually produces a litter of four capybara babies, but may produce between one and eight in a single litter. Birth is on land and the female will rejoin the group within a few hours of delivering the newborn capybaras, which will join the group as soon as they are mobile. Within a week, the young can eat grass, but will continue to suckle—from any female in the group—until weaned at about 16 weeks. The young will form a group within the main group. Alloparenting has been observed in this species. Breeding peaks between April and May in Venezuela and between October and November in Mato Grosso, Brazil.
Though quite agile on land (capable of running as fast as a horse), Capybaras are equally at home in the water. They are excellent swimmers, and can remain completely submerged for up to five minutes, an ability they use to evade predators. Capybaras can sleep in water if need be, only keeping their noses out of the water. During midday, as temperatures increase, they wallow in water and then graze in late afternoons and early evenings. They also spend a lot of time wallowing in mud. They rest around midnight and then continue to graze before dawn.
Conservation and human interaction 
Capybaras are hunted for their meat and pelts in some areas, and otherwise killed by humans who see their grazing as competition for livestock. In some areas, they are farmed, which has the effect of ensuring the wetland habitats are protected. Their survival is aided by their ability to breed rapidly.
The European Association of Zoos and Aquaria (EAZA) tasked Drusillas Park in Alfriston, Sussex to keep the studbook for Capybaras, to monitor captive populations in Europe. The studbook includes information about all births, deaths and movements of capybaras, as well as how they are related.
Capybara are farmed for meat and skins in South America. The meat is considered unsuitable to eat in some areas, while in other areas it is considered an important source of protein. During Lent, capybara meat is especially popular in parts of South America, especially in Venezuela, as the Catholic Church, in a special dispensation, is claimed to have allowed eating capybara meat when meat consumption was otherwise not allowed. Accounts differ of how the dispensation arose. Although it is illegal in some states, capybaras are occasionally kept as pets in the United States.
See also 
- Josephoartigasia monesi, an extinct species identified as the largest rodent ever
- In medicine, see Kurloff cells
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