rabbits

Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit species and its descendants, the world's 305 breeds of domestic rabbit. ''Sylvilagus'' includes 13 wild rabbit species, among them the seven types of cottontail. The European rabbit, which has been introduced on every continent except Antarctica, is familiar throughout the world as a wild prey animal and as a domesticated form of livestock and pet. With its widespread effect on ecologies and cultures, the rabbit is, in many areas of the world, a part of daily life—as food, clothing, a companion, and a source of artistic inspiration.

Although once considered rodents, lagomorphs like rabbits have been discovered to have diverged separately and earlier than their rodent cousins and have a number of traits rodents lack, like two extra incisors.

Terminology and etymology

A male rabbit is called a ''buck''; a female is called a ''doe''. An older term for an adult rabbit used until the 18th century is ''coney'' (derived ultimately from the Latin ), while ''rabbit'' once referred only to the young animals. Another term for a young rabbit is ''bunny'', though this term is often applied informally (particularly by children) to rabbits generally, especially domestic ones. More recently, the term ''kit'' or ''kitten'' has been used to refer to a young rabbit.

A group of rabbits is known as a ''colony'' or ''nest'' (or, occasionally, a ''warren'', though this more commonly refers to where the rabbits live). A group of baby rabbits produced from a single mating is referred to as a ''litter'' and a group of domestic rabbits living together is sometimes called a ''herd''.

The word rabbit itself derives from the Middle English , a borrowing from the Walloon , which was a diminutive of the French or Middle Dutch .

Taxonomy

Rabbits and hares were formerly classified in the order Rodentia (rodent) until 1912, when they were moved into a new order, Lagomorpha (which also includes pikas). Below are some of the genera and species of the rabbit.

File:BRACHYLAGUS IDAHOENSIS.jpg, alt=A small, round, dust-coloured rabbit with upright, close-set ears sat on the ground amidst dead branches., ''Brachylagus idahoensis''Pygmy rabbit
File:Sumatran Striped Rabbit Recontruction.jpg, alt=A model of a relatively large rabbit, with a slightly longer face and shorter, rounder ears, and fur patterned black and gold., ''Nesolagus netscheri''Sumatran Striped Rabbit''(Model)''
File:Oryctolagus cuniculus Tasmania 2.jpg, alt=A small, light-brown rabbit with upright ears sat on some grass., ''Oryctolagus cuniculus''European rabbit''(Feral Tasmanian specimen)''
File:Amami rabbit Stuffed specimen.jpg, alt=A taxidermy of a large rabbit with dark brown fur, small, thin ears and an elongated, rodent-like face., ''Pentalagus furnessi''Amami rabbit''(Taxidermy specimen)''
File:Taxidermied romerolagus diazi.JPG, alt=A taxidermy of a very small light-brown rabbit mid-gallop. Its features are equally small, appearing similar to a vole., ''Romerolagus diazi''Volcano rabbit''(Taxidermy specimen)''
File:Southern swamp rabbit baby.jpg, alt=A juvenile rabbit sat on a white person's hand; its fur is a light brown ticked heavily with dark brown. It is not quite large enough to fill the person's hand completely., ''Sylvilagus aquaticus''Swamp rabbit''(Juvenile)''
File:What's Up Doc.jpg, alt=A medium-sized rabbit with light brown fur ticked with grey, its ears large and upright. It stands on all fours on some sandy ground., ''Sylvilagus audubonii''Desert cottontail
File:Sylvilagus bachmani 01035t.JPG, alt=A light-brown rabbit sitting in a field, its body unusually large and squat, its limbs and head small, and its ears especially small, ''Sylvilagus bachmani''Brush rabbit
File:Sylvilagus brasiliensis meridensis (Sylvilagus meridensis) - Museo Civico di Storia Naturale Giacomo Doria - Genoa, Italy - DSC02875.JPG, alt=A taxidermy of a small rabbit, its fur a warm brown ticked with a darker brown, its ears small and set back, its face closer to a vole's than a rabbit's , ''Sylvilagus brasiliensis''Tapeti''(Taxidermy specimen)''
File:Eastern Cottontail.JPG, alt=A rabbit sitting upright in a field, turning to face the camera, its fur a light brown ticked with grey and dark brown, its ears upright , ''Sylvilagus floridanus''Eastern cottontail

* Order Lagomorpha
** Family Leporidae (in part)
* Genus '' Brachylagus''
** Pygmy rabbit, ''Brachylagus idahoensis''
* Genus ''Bunolagus''
** Bushman rabbit, ''Bunolagus monticularis''
* Genus ''Lepus''
* Genus '' Nesolagus''
** Sumatran striped rabbit, ''Nesolagus netscheri''
** Annamite striped rabbit, ''Nesolagus timminsi''
* Genus '' Oryctolagus''
** European rabbit, ''Oryctolagus cuniculus''
* Genus ''Pentalagus''
** Amami rabbit/Ryūkyū rabbit, ''Pentalagus furnessi''
* Genus '' Poelagus''
** Central African Rabbit, ''Poelagus marjorita''
* Genus ''Romerolagus''
** Volcano rabbit, ''Romerolagus diazi''
* Genus ''Sylvilagus''
** Swamp rabbit, ''Sylvilagus aquaticus''
** Desert cottontail, ''Sylvilagus audubonii''
** Brush rabbit, ''Sylvilagus bachmani''
** Forest rabbit, ''Sylvilagus brasiliensis''
** Mexican cottontail, ''Sylvilagus cunicularis''
** Dice's cottontail, ''Sylvilagus dicei''
** Eastern cottontail, ''Sylvilagus floridanus''
** Tres Marias rabbit, ''Sylvilagus graysoni''
** Omilteme cottontail, ''Sylvilagus insonus''
** San Jose brush rabbit, ''Sylvilagus mansuetus''
** Mountain cottontail, ''Sylvilagus nuttallii''
** Marsh rabbit, ''Sylvilagus palustris''
** New England cottontail, ''Sylvilagus transitionalis''

Differences from hares

The term "rabbit" is typically used for all Leporidae species excluding the genus ''Lepus''. Members of that genus are instead known as hares or jackrabbits.

''Lepus'' species are typically precocial, born relatively mature and mobile with hair and good vision, while rabbit species are altricial, born hairless and blind, and requiring closer care. Hares live a relatively solitary life in a simple nest above the ground, while most rabbits live in social groups in burrows or warrens. Hares are generally larger than rabbits, with ears that are more elongated, and with hind legs that are larger and longer. Descendants of the European rabbit are commonly bred as livestock and kept as pets, whereas no hares have been domesticated - the breed called the Belgian hare is actually a domestic rabbit which has been selectively bred to resemble a hare.

Domestication

Rabbits have long been domesticated. Beginning in the Middle Ages, the European rabbit has been widely kept as livestock, starting in ancient Rome. Selective breeding has generated a wide variety of rabbit breeds, of which many (since the early 19th century) are also kept as pets. Some strains of rabbit have been bred specifically as research subjects.

As livestock, rabbits are bred for their meat and fur. The earliest breeds were important sources of meat, and so became larger than wild rabbits, but domestic rabbits in modern times range in size from dwarf to giant. Rabbit fur, prized for its softness, can be found in a broad range of coat colors and patterns, as well as lengths. The Angora rabbit breed, for example, was developed for its long, silky fur, which is often hand-spun into yarn. Other domestic rabbit breeds have been developed primarily for the commercial fur trade, including the Rex, which has a short plush coat.

Biology

Evolution

Because the rabbit's epiglottis is engaged over the soft palate except when swallowing, the rabbit is an obligate nasal breather. Rabbits have two sets of incisor teeth, one behind the other. This way they can be distinguished from rodents, with which they are often confused. Carl Linnaeus originally grouped rabbits and rodents under the class Glires; later, they were separated as the scientific consensus is that many of their similarities were a result of convergent evolution. Recent DNA analysis and the discovery of a common ancestor has supported the view that they share a common lineage, so rabbits and rodents are now often grouped together in the superorder Glires.

Morphology

Since speed and agility are a rabbit's main defenses against predators (including the swift fox), rabbits have large hind leg bones and well developed musculature. Though plantigrade at rest, rabbits are on their toes while running, assuming a more digitigrade posture. Rabbits use their strong claws for digging and (along with their teeth) for defense. Each front foot has four toes plus a dewclaw. Each hind foot has four toes (but no dewclaw).

Most wild rabbits (especially compared to hares) have relatively full, egg-shaped bodies. The soft coat of the wild rabbit is agouti in coloration (or, rarely, melanistic), which aids in camouflage. The tail of the rabbit (with the exception of the cottontail species) is dark on top and white below. Cottontails have white on the top of their tails.

As a result of the position of the eyes in its skull, the rabbit has a field of vision that encompasses nearly 360 degrees, with just a small blind spot at the bridge of the nose.

Hind limb elements

The anatomy of rabbits' hind limbs are structurally similar to that of other land mammals and contribute to their specialized form of locomotion. The bones of the hind limbs consist of long bones (the femur, tibia, fibula, and phalanges) as well as short bones (the tarsals). These bones are created through endochondral ossification during development. Like most land mammals, the round head of the femur articulates with the acetabulum of the os coxae. The femur articulates with the tibia, but not the fibula, which is fused to the tibia. The tibia and fibula articulate with the tarsals of the pes, commonly called the foot. The hind limbs of the rabbit are longer than the front limbs. This allows them to produce their hopping form of locomotion. Longer hind limbs are more capable of producing faster speeds. Hares, which have longer legs than cottontail rabbits, are able to move considerably faster. Rabbits stay just on their toes when moving; this is called Digitigrade locomotion. The hind feet have four long toes that allow for this and are webbed to prevent them from spreading when hopping. Rabbits do not have paw pads on their feet like most other animals that use digitigrade locomotion. Instead, they have coarse compressed hair that offers protection.

Musculature

Rabbits have muscled hind legs that allow for maximum force, maneuverability, and acceleration that is divided into three main parts; foot, thigh, and leg. The hind limbs of a rabbit are an exaggerated feature. They are much longer than the forelimbs, providing more force. Rabbits run on their toes to gain the optimal stride during locomotion. The force put out by the hind limbs is contributed to both the structural anatomy of the fusion tibia and fibula, and muscular features. Bone formation and removal, from a cellular standpoint, is directly correlated to hind limb muscles. Action pressure from muscles creates force that is then distributed through the skeletal structures. Rabbits that generate less force, putting less stress on bones are more prone to osteoporosis due to bone rarefaction. In rabbits, the more fibers in a muscle, the more resistant to fatigue. For example, hares have a greater resistance to fatigue than cottontails. The muscles of rabbit's hind limbs can be classified into four main categories: hamstrings, quadriceps, dorsiflexors, or plantar flexors. The quadriceps muscles are in charge of force production when jumping. Complementing these muscles are the hamstrings, which aid in short bursts of action. These muscles play off of one another in the same way as the plantar flexors and dorsiflexors, contributing to the generation and actions associated with force.

Ears

Within the order lagomorphs, the ears are utilized to detect and avoid predators. In the family Leporidae, the ears are typically longer than they are wide. For example, in black tailed jack rabbits, their long ears cover a greater surface area relative to their body size that allow them to detect predators from far away. Contrasted to cotton tailed rabbits, their ears are smaller and shorter, requiring predators to be closer to detect them before they can flee. Evolution has favored rabbits having shorter ears so the larger surface area does not cause them to lose heat in more temperate regions. The opposite can be seen in rabbits that live in hotter climates, mainly because they possess longer ears that have a larger surface area that help with dispersion of heat as well as the theory that sound does not travel well in more arid air, opposed to cooler air. Therefore, longer ears are meant to aid the organism in detecting predators sooner rather than later in warmer temperatures. The rabbit is characterized by its shorter ears while hares are characterized by their longer ears. Rabbits' ears are an important structure to aid thermoregulation and detect predators due to how the outer, middle, and inner ear muscles coordinate with one another. The ear muscles also aid in maintaining balance and movement when fleeing predators.

Outer ear

The auricle, also known as the pinna, is a rabbit's outer ear. The rabbit's pinnae represent a fair part of the body surface area. It is theorized that the ears aid in dispersion of heat at temperatures above 30 °C with rabbits in warmer climates having longer pinnae due to this. Another theory is that the ears function as shock absorbers that could aid and stabilize rabbit's vision when fleeing predators, but this has typically only been seen in hares. The rest of the outer ear has bent canals that lead to the eardrum or tympanic membrane.

Middle ear

The middle ear is filled with three bones called ossicles and is separated by the outer eardrum in the back of the rabbit's skull. The three ossicles are called hammer, anvil, and stirrup and act to decrease sound before it hits the inner ear. In general, the ossicles act as a barrier to the inner ear for sound energy.

Inner ear

Inner ear fluid called endolymph receives the sound energy. After receiving the energy, later within the inner ear there are two parts: the cochlea that utilizes sound waves from the ossicles and the vestibular apparatus that manages the rabbit's position in regards to movement. Within the cochlea there is a basilar membrane that contains sensory hair structures utilized to send nerve signals to the brain so it can recognize different sound frequencies. Within the vestibular apparatus the rabbit possesses three semicircular canals to help detect angular motion.

Thermoregulation

Thermoregulation is the process that an organism utilizes to maintain an optimal body temperature independent of external conditions. This process is carried out by the pinnae, which takes up most of the rabbit's body surface and contain a vascular network and arteriovenous shunts. In a rabbit, the optimal body temperature is around 38.5–40℃. If their body temperature exceeds or does not meet this optimal temperature, the rabbit must return to homeostasis. Homeostasis of body temperature is maintained by the use of their large, highly vascularized ears that are able to change the amount of blood flow that passes through the ears.

Constriction and dilation of blood vessels in the ears are used to control the core body temperature of a rabbit. If the core temperature exceeds its optimal temperature greatly, blood flow is constricted to limit the amount of blood going through the vessels. With this constriction, there is only a limited amount of blood that is passing through the ears where ambient heat would be able to heat the blood that is flowing through the ears and therefore, increasing the body temperature. Constriction is also used when the ambient temperature is much lower than that of the rabbit's core body temperature. When the ears are constricted it again limits blood flow through the ears to conserve the optimal body temperature of the rabbit. If the ambient temperature is either 15 degrees above or below the optimal body temperature, the blood vessels will dilate. With the blood vessels being enlarged, the blood is able to pass through the large surface area, causing it to either heat or cool down.

During hot summers, the rabbit has the capability to stretch its pinnae, which allows for greater surface area and increase heat dissipation. In cold winters, the rabbit does the opposite and folds its ears in order to decrease its surface area to the ambient air, which would decrease their body temperature.

The jackrabbit has the largest ears within the ''Oryctolagus cuniculus'' group. Their ears contribute to 17% of their total body surface area. Their large pinna were evolved to maintain homeostasis while in the extreme temperatures of the desert.

Respiratory system

The rabbit's nasal cavity lies dorsal to the oral cavity, and the two compartments are separated by the hard and soft palate. The nasal cavity itself is separated into a left and right side by a cartilage barrier, and it is covered in fine hairs that trap dust before it can enter the respiratory tract. As the rabbit breathes, air flows in through the nostrils along the alar folds. From there, the air moves into the nasal cavity, also known as the nasopharynx, down through the trachea, through the larynx, and into the lungs. The larynx functions as the rabbit's voice box, which enables it to produce a wide variety of sounds. The trachea is a long tube embedded with cartilaginous rings that prevent the tube from collapsing as air moves in and out of the lungs. The trachea then splits into a left and right bronchus, which meet the lungs at a structure called the hilum. From there, the bronchi split into progressively more narrow and numerous branches. The bronchi branch into bronchioles, into respiratory bronchioles, and ultimately terminate at the alveolar ducts. The branching that is typically found in rabbit lungs is a clear example of monopodial branching, in which smaller branches divide out laterally from a larger central branch.

The structure of the rabbit's nasal and oral cavities, necessitates breathing through the nose. This is due to the fact that the epiglottis is fixed to the backmost portion of the soft palate. Within the oral cavity, a layer of tissue sits over the opening of the glottis, which blocks airflow from the oral cavity to the trachea. The epiglottis functions to prevent the rabbit from aspirating on its food. Further, the presence of a soft and hard palate allow the rabbit to breathe through its nose while it feeds.

Rabbits lungs are divided into four lobes: the cranial, middle, caudal, and accessory lobes. The right lung is made up of all four lobes, while the left lung only has two: the cranial and caudal lobes. In order to provide space for the heart, the left cranial lobe of the lungs is significantly smaller than that of the right. The diaphragm is a muscular structure that lies caudal to the lungs and contracts to facilitate respiration.

Digestion

Rabbits are herbivores that feed by grazing on grass and other leafy plants. Consequently, their diet contains large amounts of cellulose, which is hard to digest. Rabbits solve this problem via a form of hindgut fermentation

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