At over a metre in length and weighing as much as an adult human, the capybara is the largest rodent in the world. A stocky, somewhat pig-like animal, it is characterised by a large, blunt head, heavy muzzle, short, robust legs and rudimentary tail (2) (3) (4). The hair is coarse and sparse, and varies in colour between dark brown, reddish and yellowish brown (2) (3) (5), occasionally with some black on the face, the outer surface of the limbs, and on the rump (4) (6). The capybara shows a number of adaptations to a partly aquatic lifestyle. It is able to swim with only the nostrils, eyes and short, rounded ears protruding out of the water, as they are placed high on the head (3) (4) (7), and the body contains a large amount of fatty tissue, giving it a neutral buoyancy in water (6). The feet are also partially webbed. Each of the forefeet has four toes, while the hindfeet have only three, and each toe bears a strong, hoof-like claw (2) (4) (5). The capybara often sits on its haunches like a dog, but, unlike many other rodents, is unable to hold food in its forefeet (2). The male capybara can be distinguished from the female by the obvious, highly developed scent gland on top of the snout. Known as a morillo
, this dark, naked, raised area secrete a copious white, sticky fluid, thought to be involved in signalling dominance status (3) (4). In addition to using scent, the capybara also communicates through a variety of vocalisations, including growls, whinnies, alarm barks, whistles, and a constant guttural purr emitted by the infant (2) (3) (4). This species is distinguished from the lesser capybara, Hydrochoerus isthmius
, by its larger size (5), although there is some confusion over the distributional boundaries of these species (1).