The family Caviidae contains six genera and 20 species, plus one domesticated species. There are three subfamilies: Caviinae (Guinea pigs, Cavia; yellow-toothed cavies, Galea; mountain cavies, Microcavia), Hydrochoerinae (capybaras, Hydrochoerus; rock cavies, Kerodon), and Dolichotinae (maras, Dolichotis). Caviids are medium to large-sized rodents with compact bodies, short limbs, and big heads, with the Greater capybara being the largest rodent in the world. The earliest caviid fossil comes from the Miocene in South America, and the emergence of the clade Cavioidea appeared 26-28 million years ago.
All species in the subfamilies of Caviinae and Hydrochoerine are tailless and have large heads, with three toes on the hind feet and four toes on the forefeet. In Caviinae, the digits are clawed, but the digits in Hydrochoerine are smoothed nails. There is great variability in the subfamily Dolichotinae. The heads of these species are large when compared to their bodies, and they have three large hoof-like toes on the hind feet and four toes with sharp claws on the forefeet. All caviids have the same dental formula, with teeth that never stop growing, and all possess enlarged infraorbital foramen. Galea species have distinctive yellow incisors and less complex cusp patterns than Cavia. The teeth of Microcavia are similar to Galea, and have the largest bullae compared to the cranium out of the three genera. Dolichotis skulls are more compressed with broad frontal bones and specialized nasals that do not reach the premaxillae.
Caviids mostly live in arid and semiarid open habitats, but when in forested areas, live near rivers and open patches. The Patagonian mara lives in grasslands and steppe formations in Southern Argentina, while the Chacoan mara inhabits thorn-scrub areas of the Argentine, Bolivian and Paraguayan Chaco. Microcavia mountain cavies also live in arid and semiarid open formations and favor high-elevated regions of Bolivia, Chile, and Argentina. Cavia species have a broad distribution, with the Brazilian guinea pig living in high-elevation grasslands of western South America to the Llanos grasslands in Venezuela. Other guinea pigs live in grassy, open regions in eastern Brazil. In the Hydrochoerines, the Rock cavy occurs in rock outcrops in semiarid caatinga, and the Acrobatic cavy is restricted to the dry cerrado forest limestone outcrops. Both the Greater capybara and the Lesser capybara inhabit semi-aquatic regions near bodies of water. The locomotion of Caviidae is highly terrestrial in guinea pigs and yellow-toothed cavies, cursorial in maras, scansorial in mountain cavies, semiarboreal in cavies, and semi-aquatic in capybaras. All caviids are active throughout the year, but peak during twilight. Predators include the Tayra, the Lesser grison, the Greater grison, small cats, and foxes. Pumas and jaguars also prey on capybaras.
Caviids are social creatures that have many forms of communication relating to their social organization, including vocal sounds and specialized scent glands used by dragging the anus on the ground. When threatened, the Southern mountain cavy makes a short “tsit” sound before running away, and the capybara barks when scared. The Rock cavy begins its alarm call as a low sound that increases into a piercing whistle. Some other noises include the capybara’s purr, the cavy’s and mara’s whistle, the yellow-toothed cavy’s chirp, and the mountain cavy’s shriek.
All species of Caviidae are herbivores and eat grasses, with some browsing. Guinea pigs and yellow-toothed cavies also consume small forbs, while mountain cavies rely on desert shrubs since they live in arid climates. Both species of mara also consume the fruits of shrubs, and capybaras eat the green vegetation along wetlands and riverbanks. Rock cavies have the most varied diet because they forage on leaves, flowers, fruits, bark, and branches of shrubs and trees. Since grasses contain indigestible cellulose, all caviids exhibit coprophagy, which is the re-ingestion of fecal matter to absorb all of the nutrients.
Caviids give birth to precocial young, who are born with open eyes and the ability to walk right after birth. Litter sizes are usually smaller in species living in arid regions, while larger species have longer gestation periods. Smaller species like mountain cavies reach sexual maturity at 40-50 days, and larger species like capybaras reach sexual maturity at around 18 months. Data on the life spans of caviids is sparse, but the species living in captivity live longer than the wild species. Tropical species, like capybaras, breed throughout the year, but species living in arid zones show some seasonal variation in reproduction. Their mating system is classified as promiscuous, but the Brazilian guinea pig has been described as harem-based with little promiscuity. The males are heavier than the females, and young males wait for the chance to replace the dominant male. The Highland and Lowland yellow-toothed cavies are solitary and most likely promiscuous, with the home ranges of males being five times larger than the females’ home ranges. The males and females of Spix’s yellow-toothed cavy are both aggressive and do not exhibit social grooming or contact. Mountain cavies have been described as promiscuous and polygynous. The males and females of the Patagonian mara form pair bonds and defend their burrows. Species of Hydrochoerinae exhibit a form of polygyny based on defending limited resources by a dominant male, which allows males to gain mates that aggregate around the resource. In Kerodon species, this limited resource is boulder piles found in northeastern Brazil. Male rock cavies defend clusters of rock and alert the harem of females when there is a threat. Capybaras defend temporary pools and bodies of water, with males maintaining a strong dominance hierarchy.
In general, caviids are not significant crop pests. They are hunted for food and for leather, even though hunting is illegal in most of Brazil, except for subsistence by the indigenous population. Kerodon are highly prized as a protein source in northeastern Brazil, and capybaras are hunted for their leather, which is used in the manufacturing of gloves, slippers, and jackets in Argentina. The domestic guinea pig was derived from the Montane guinea pig from the Andean highlands and is considered an important source of protein in Peru and Bolivia, as 65 million domestic guinea pigs are eaten annually in Peru alone. Most caviids are tolerant to some habitat disturbance since they can live in a mosaic of landscapes. Shipton’s mountain cavy is classified as Near Threatened on the IUCN Red List and the Santa Catarina’s guinea pig is Critically Endangered and is one of the rarest mammals in the world since it only lives in an area of less than 10-hectares on Moleques do Sul Island off the Brazilian coast, with a population of only 42 individuals. The Patagonian mara is Near Threatened because of habitat degradation and competition with livestock, but the rest of the caviid species are Least Concern or Data Deficient.
Author: Sidney Sanchez