Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genera in the family classified as rabbits, including the European rabbit (Oryctolagus cuniculus), Cottontail rabbit (genus Sylvilagus; 13 species), and the Amami rabbit (Pentalagus furnessi, endangered species on Amami Ōshima, Japan). There are many other species of rabbit, and these, along with pikas and hares, make up the order Lagomorpha.Location and habitat
Rabbits are ground dwellers that live in environments ranging from desert to tropical forest and wetland. Their natural geographic range encompasses the middle latitudes of the Western Hemisphere. In the Eastern Hemisphere rabbits are found in Europe, portions of Central and Southern Africa, the Indian subcontinent, Sumatra, and Japan. The European rabbit (Oryctolagus cuniculus) has been introduced to many locations around the world, and all breeds of domestic rabbit originate from the European.
Characteristics and anatomy
The long ears of rabbits are most likely an adaptation for detecting predators. In addition to their prominent ears, which can measure more than 10 cm (4 in) long, rabbits have long, powerful hind legs and a short tail. Each foot has five digits (one reduced); rabbits move about on the tips of the digits in a fashion known as digitigrade locomotion. Full-bodied and egg-shaped, wild rabbits are rather uniform in body proportions and stance. The smallest is the pygmy rabbit (Brachylagus idahoensis), at only 20 cm in length and 0.4 kg (0.9 pound) in weight, while the largest grow to 50 cm and more than 2 kg. The fur is generally long and soft, and its color ranges through shades of brown, gray, and buff. Exceptions are the black Amami rabbit (Pentalagus furnessi) of Japan and two black-striped species from Southeast Asia. The tail is usually a small puff of fur, generally brownish but white on top in the cottontails (genus Sylvilagus) of North and South America.
Cecal pellets
Rabbits are hindgut digesters. This means that most of their digestion takes place in their large intestine and cecum. In rabbits, the cecum is about 10 times bigger than the stomach, and it, along with the large intestine, makes up roughly 40% of the rabbit's digestive tract. Cecotropes, sometimes called "night feces", come from the cecum and are high in minerals, vitamins and proteins that are necessary to the rabbit's health. Rabbits eat these to meet their nutritional requirements. This process allows rabbits to extract the necessary nutrients from their food.
Diet and eating habits
Rabbits are herbivores who feed by grazing on grass, forbs, and leafy weeds. In consequence, their diet contains large amounts of cellulose, which is hard to digest. Rabbits solve this problem by passing two distinct types of feces: hard droppings and soft black viscous pellets, the latter of which are immediately eaten. Rabbits reingest their own droppings (rather than chewing the cud as do cows and many other herbivores) to digest their food further and extract sufficient nutrients.
Rabbits graze heavily and rapidly for roughly the first half hour of a grazing period (usually in the late afternoon), followed by about half an hour of more selective feeding. In this time, the rabbit will also excrete many hard fecal pellets, being waste pellets that will not be reingested. If the environment is relatively non-threatening, the rabbit will remain outdoors for many hours, grazing at intervals. While out of the burrow, the rabbit will occasionally reingest its soft, partially digested pellets; this is rarely observed, since the pellets are reingested as they are produced. Reingestion is most common within the burrow between 8 o'clock in the morning and 5 o'clock in the evening, being carried out intermittently within that period.
Hard pellets are made up of hay-like fragments of plant cuticle and stalk, being the final waste product after redigestion of soft pellets. These are only released outside the burrow and are not reingested. Soft pellets are usually produced several hours after grazing, after the hard pellets have all been excreted. They are made up of micro-organisms and undigested plant cell walls.
The chewed plant material collects in the large cecum, a secondary chamber between the large and small intestine containing large quantities of symbiotic bacteria that help with the digestion of cellulose and also produce certain B vitamins. The pellets are about 56% bacteria by dry weight, largely accounting for the pellets being 24.4% protein on average. These pellets remain intact for up to six hours in the stomach; the bacteria within continue to digest the plant carbohydrates. The soft feces form here and contain up to five times the vitamins of hard feces. After being excreted, they are eaten whole by the rabbit and redigested in a special part of the stomach. This double-digestion process enables rabbits to use nutrients that they may have missed during the first passage through the gut, and thus ensures that maximum nutrition is derived from the food they eat. This process serves the same purpose within the rabbit as rumination does in cattle and sheep.
Rabbits are incapable of vomiting due to the physiology of their digestive system.
Behavior
While the European rabbit is the best-known species, it is probably also the least typical, as there is considerable variability in the natural history of rabbits. Many rabbits dig burrows, but cottontails and hispid hares do not. The European rabbit constructs the most extensive burrow systems, called warrens. Nonburrowing rabbits make surface nests called forms, generally under dense protective cover. The European rabbit occupies open landscapes such as fields, parks, and gardens, although it has colonized habitats from stony deserts to subalpine valleys. It is the most social rabbit, sometimes forming groups in warrens of up to 20 individuals. However, even in European rabbits, social behaviour can be quite flexible, depending on habitat and other local conditions, so that at times the primary social unit is a territorial breeding pair. Most rabbits are relatively solitary and sometimes territorial, coming together only to breed or occasionally to forage in small groups. During territorial disputes rabbits will sometimes “box,” using their front limbs. Rabbits are active throughout the year; no species is known to hibernate. Rabbits are generally nocturnal, and they also are relatively silent. Other than loud screams when frightened or caught by a predator, the only auditory signal known for most species is a loud foot thump made to indicate alarm or aggression. Notable exceptions are the Amami rabbit and the volcano rabbit of Mexico, which both utter a variety of calls.
Instead of sound, scent seems to play a predominant role in the communication systems of most rabbits; they possess well-developed glands throughout their body and rub them on fixed objects to convey group identity, sex, age, social and reproductive status, and territory ownership. Urine is also used in chemical communication. When danger is perceived, the general tendency of rabbits is to freeze and hide under cover. If chased by a predator, they engage in quick, irregular movement, designed more to evade and confuse than to outdistance a pursuer. Skeletal adaptations such as long hind limbs and a strengthened pelvic girdle enable their agility and speed (up to 48 km [30 miles] per hour).
Diet and eating habits
Rabbits are herbivores who feed by grazing on grass, forbs, and leafy weeds. In consequence, their diet contains large amounts of cellulose, which is hard to digest. Rabbits solve this problem by passing two distinct types of feces: hard droppings and soft black viscous pellets, the latter of which are immediately eaten. Rabbits reingest their own droppings (rather than chewing the cud as do cows and many other herbivores) to digest their food further and extract sufficient nutrients.
Rabbits graze heavily and rapidly for roughly the first half hour of a grazing period (usually in the late afternoon), followed by about half an hour of more selective feeding. In this time, the rabbit will also excrete many hard fecal pellets, being waste pellets that will not be reingested. If the environment is relatively non-threatening, the rabbit will remain outdoors for many hours, grazing at intervals. While out of the burrow, the rabbit will occasionally reingest its soft, partially digested pellets; this is rarely observed, since the pellets are reingested as they are produced. Reingestion is most common within the burrow between 8 o'clock in the morning and 5 o'clock in the evening, being carried out intermittently within that period.
Hard pellets are made up of hay-like fragments of plant cuticle and stalk, being the final waste product after redigestion of soft pellets. These are only released outside the burrow and are not reingested. Soft pellets are usually produced several hours after grazing, after the hard pellets have all been excreted. They are made up of micro-organisms and undigested plant cell walls.
The chewed plant material collects in the large cecum, a secondary chamber between the large and small intestine containing large quantities of symbiotic bacteria that help with the digestion of cellulose and also produce certain B vitamins. The pellets are about 56% bacteria by dry weight, largely accounting for the pellets being 24.4% protein on average. These pellets remain intact for up to six hours in the stomach; the bacteria within continue to digest the plant carbohydrates. The soft feces form here and contain up to five times the vitamins of hard feces. After being excreted, they are eaten whole by the rabbit and redigested in a special part of the stomach. This double-digestion process enables rabbits to use nutrients that they may have missed during the first passage through the gut, and thus ensures that maximum nutrition is derived from the food they eat. This process serves the same purpose within the rabbit as rumination does in cattle and sheep.
Rabbits are incapable of vomiting due to the physiology of their digestive system.
Behavior
While the European rabbit is the best-known species, it is probably also the least typical, as there is considerable variability in the natural history of rabbits. Many rabbits dig burrows, but cottontails and hispid hares do not. The European rabbit constructs the most extensive burrow systems, called warrens. Nonburrowing rabbits make surface nests called forms, generally under dense protective cover. The European rabbit occupies open landscapes such as fields, parks, and gardens, although it has colonized habitats from stony deserts to subalpine valleys. It is the most social rabbit, sometimes forming groups in warrens of up to 20 individuals. However, even in European rabbits, social behaviour can be quite flexible, depending on habitat and other local conditions, so that at times the primary social unit is a territorial breeding pair. Most rabbits are relatively solitary and sometimes territorial, coming together only to breed or occasionally to forage in small groups. During territorial disputes rabbits will sometimes “box,” using their front limbs. Rabbits are active throughout the year; no species is known to hibernate. Rabbits are generally nocturnal, and they also are relatively silent. Other than loud screams when frightened or caught by a predator, the only auditory signal known for most species is a loud foot thump made to indicate alarm or aggression. Notable exceptions are the Amami rabbit and the volcano rabbit of Mexico, which both utter a variety of calls.
Instead of sound, scent seems to play a predominant role in the communication systems of most rabbits; they possess well-developed glands throughout their body and rub them on fixed objects to convey group identity, sex, age, social and reproductive status, and territory ownership. Urine is also used in chemical communication. When danger is perceived, the general tendency of rabbits is to freeze and hide under cover. If chased by a predator, they engage in quick, irregular movement, designed more to evade and confuse than to outdistance a pursuer. Skeletal adaptations such as long hind limbs and a strengthened pelvic girdle enable their agility and speed (up to 48 km [30 miles] per hour).
