Once called called “water pigs” or “Orinoco hogs” by the first European naturalists visiting South America, the capybara is neither a pig nor a fully aquatic animal. But this wacky Wednesday special is, indeed, LARGEST LIVING RODENT (110 lb or 50 kg). They are hydrochoerids with its nearest living relative being the cavies. All other hydrochoerids are extinct, but all of them were significantly larger than the capybara with the largest one weighing more than the largest North American grizzly bear (over 800 lb)! But what successful features of the capybara allowed it to survive? Could it be sexual or it’s “smaller” size?
Studies have shown that animals actually decrease in size as temperatures warm, which occurred after the last ice age. So this may have been a contributing factor to the success of this “smaller” hydrochoerid.
Capybaras also have two types of scent glands: one that is very developed in males and practically nonexistent in females located on the top of the snout called the “morrillo”. It produces an opaque sticky, beige fluid that when squeezed out seems “overflows the cup”. Both sexes produce odors from two anal glands. Male anal glands are covered with detachable hairs that coat hard calcium salts, while female anal glands do not have detachable hairs (theirs stay wrenched in) and are coated in an oily secretion rather than crystalline one. What is most interesting is that capybaras seem to have “olfactory fingerprints”: each individual secretes different concentrations of these fluids allowing for individual recognition. It is thought that the snout scent gland is used to demarcate and signal dominance while the anal gland is used for recognition and thus let others know whose territory they are about to step into.
These savanna-dwelling, water-loving social grazers have no tail, are tootsie-roll shaped, have shorter front legs, and have web-toes with only 4 toes on the front feet and 3 on the back ones. These traits make them exceptionally strong swimmers. Their eyes, nostrils, and ears are all situated on the top of their head in order to allow them to swim and poke their heads out of the water to breathe efficiently while swimming.
Perhaps one of the most unique features of the capybara is how it eats by recycling cellulose! They are exclusively herbivorous, eating short grasses that they find near the water. One of main components of grass is cellulose, which is indigestible to mammals. In order to take advantage of this food, their digestive system has been modified to accommodate a huge cecum, which is a modified fermentation vat. Where ruminants, such as cows, use microbial aids for digestion in their four-chambered stomach, the capybara simply cannot use microbes quite as efficiently since the cecum is located between the small and large intestine. So what do they do? To solve “zis petite problemme”, the capybara utilizes the practice of coprophagy- reingestion of feces. Thus the symbionts (bacteria just waiting to eat up and give the capybara their waste products) get two intakes of the food: one for the first digestion and then one for a second one during which the capybaras recycles what they ate the previous evening and night. Basically: they re-eat their poo.
*Some of you may be thinking “bunnies!” right now, and that is totally correct: although rabbits and bunnies are not rodents (rather they are lagomorphs), they also have a large cecum and employ the use of coprophagy.
Back to capybaras: they spend the morning resting and recycling, and then they bathe during the very hot South American midday- the Spanish ciesta influenced them before the Spanish arrived, it seems! During the cooler late afternoons/early evenings, capybaras graze. These giant rodents don’t really “sleep”. Rather they just take a bunch of “power naps” throughout the day.
As humans, I think we can relate a little bit to the social structure of capybaras: they form cliques, which are technically called “closed social units” that consist of 10-30 critters. When the savannas are greener, more animals aggregate together, and also during the dry season (when water dries up), capybaras can live in groups up to 100! In their smaller cliques, a group is composed of a dominant male which is obvious by his very pronounced morillo, one or more females, several infants and sub-adults, and one or more insubordinate males. Males gain the status of “head honcho” by doing several skirmishes with other males. Once the dominant male, often he has to chase the subordinate males to the periphery of their territory, but rarely does he have to truly fight the “insurgent”. Females are relatively tolerant of one another, and all sexes work together to keep intruders (male or female) off their territory and out of their clique.
The breeding patterns of these curious creatures differ depending on where in South America they are located. Those from Venezuela and Columbia breed year-round, with a peak in the wet-season in May, while those in Brazil only breed once a year, which is thought to be due to its more temperate climate. Once a female goes into heat, she does a little “hello, here are my goodies” strut by walking in and out of the water while a male follows close behind her. After at least an hour of those shenanigans, they will mate in the water. Copulation only lasts a few seconds, but each one requires several mountings.
150 days later, up to seven (though four is the average) pups are born! The mother gives birth away from the group in a place of shelter. A few hours after they are born, the mother rejoins the group. Although the pups are precocial, they still must walk and follow her back. Females other than the mother share the suckling of the pups, which must be watched constantly since they tire very quickly and are prone to predation from animals such as vultures and feral dogs.
Unfortunately, the population of capybara has decreased significantly due to poaching. Both the Columbian and Venezuelan governments have implemented laws prohibiting capybara hunting, which has been better enforced in Columbia than in Venezuela. To help quell the need to kill wild capybara, 20-30% of the annually censused population of capybara in licensed ranches with populations of over 400 animals is instead now farmed.