Hamster



Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera.[1]

Hamsters are crepuscular animals which burrow underground in the daylight to avoid being caught by predators. Their diets include a variety of foods, including dried food, berries, nuts, fresh fruits and vegetables. In the wild, they feed primarily on seeds, fruits and greens, and will occasionally eat burrowing insects.[2] They have an elongated pouch on each side of their heads that extends to their shoulders, which they stuff full of food to be stored, brought back to the colony or to be eaten later.

Hamster behavior varies depending on their environment, genetics, and interaction with people. Because they are easy to breed in captivity, hamsters are often used as laboratory animals in more economically developed countries. Hamsters have also become established as popular small house pets,[3] and are sometimes accepted even in areas where other rodents are disliked, and their typically solitary nature can reduce the risk of excessive litters developing in households.

History
Although the Syrian hamster or golden hamster (Mesocricetus auratus) was first described scientifically in 1839, researchers were not able to successfully breed and domesticate hamsters until 1939.[3] The entire laboratory and pet populations of Syrian hamsters appear to be descendants of a single brother-sister pairing. These littermates were captured and imported in 1930 from Aleppo [Syria] by Israel Aharoni, a zoologist of the University of Jerusalem.[4] In Jerusalem, the hamsters bred very successfully. Years later, animals of this original breeding colony were exported to the USA, where Syrian hamsters became one of the most popular pets and laboratory animals. Comparative studies of domestic and wild Syrian hamsters have shown reduced genetic variability in the domestic strain. However, the differences in behavioral, chronobiological, morphometrical, hematological and biochemical parameters are relatively small and fall into the expected range of interstrain variations in other laboratory animals.[5]

Early literature
In 1774, Friedrich Gabriel Sulzer, a companion of Johann-Wolfgang von Goethe, devoted a whole academic monography in the domain of social sciences and natural history to hamsters, entitled "An approach to a natural history of the hamster" ("Versuch einer Naturgeschichte des Hamsters"). In several instances, he used the hamster to document the equal rights of all beings, including Homo sapiens.[6]

Etymology
The name "hamster" is a loanword from the German, which itself derives from earlier Old High German hamustro. It is possibly related to Old Russian choměstrǔ, which is either a blend of the root of Russian khomiak "hamster" and a Baltic word (cf. Lithuanian staras "hamster")[7] or of Persian origin (cf. Av hamaēstar "oppressor").[8]

Description
Roborovski hamsterHamsters are typically stout-bodied, with tails shorter than body length, and have small, furry ears, short, stocky legs, and wide feet. They have thick, silky fur, which can be long or short, colored black, grey, honey, white, brown, yellow, red, or a mix, depending on the species. Two species of hamster belonging to the genus Phodopus, Campbell's dwarf hamster (Phodopus campbelli) and the Djungarian hamster (Phodopus sungorus), and two of the genus Cricetulus, the Chinese striped hamster (Cricetulus barabensis) and the Chinese hamster (Cricetulus griseus) have a dark stripe down their heads to their tails. The species of genus Phodopus are the smallest, with bodies 5.5 to 10.5 cm (2.2 to 4.1 in) long; the largest is the European hamster (Cricetus cricetus), measuring up to 34 cm (13.4 in) long, not including a short tail of up to 6 cm (2.4 in). The Angora hamster, also known as the long-haired or teddy bear hamster, which is a type of the golden hamster is the second-largest hamster breed, measuring up to 18 cm (7.1 in) long.[3] Yawning white Syrian hamster showing large incisorsThe hamster tail can be difficult to see, as it is usually not very long (about 1/6 the length of the body), with the exception of the Chinese dwarf hamster, which has a tail the same length as the body. One rodent characteristic that can be highly visible in hamsters is their sharp incisors; they have an upper pair and lower pair which grow continuously throughout life, so must be regularly worn down. Hamsters are very flexible, but their bones are somewhat fragile. They are extremely susceptible to rapid temperature changes and drafts, as well as extreme heat or cold.

Senses
Hamsters have poor eyesight; they are nearsighted and colorblind.[citation needed] To compensate for their poor sight when in unfamiliar territory, hamsters have scent glands on their flanks (and abdomens in Chinese and dwarf hamsters). A hamster rubs these areas of its body against various objects, and leaves a trail of smells to follow to return to its home den.[citation needed] Hamsters also use their sense of smell to identify pheromones and gender, and locate food. They are also particularly sensitive to high-pitched noises and can hear and communicate in the ultrasonic range.[4]

Diet
Hamsters are omnivores. Although they can survive on a diet of exclusively commercial hamster food, other items, such as vegetables, fruits, seeds, and nuts, can be given, but these should be removed before they become rotten. Hamsters in the Middle East have been known to hunt in packs to find insects for food.[9] Hamsters are hindgut fermenters and must eat their own feces (coprophagy) to recover nutrients digested in the hindgut, but not absorbed.[1]

Behavior
A behavioral characteristic of hamsters is food hoarding. They carry food in their spacious cheek pouches to their underground storage chambers. When full, the cheeks can make their heads double, or even triple in size.[1]

Social behavior
Hamsters fightingMost hamsters are strictly solitary. If housed together, acute and chronic stress may occur,<sup class="reference" id="cite_ref-Kuhnen.2C_.282001.29_4-1">[5] and they may fight fiercely, sometimes fatally. Some dwarf hamster species may tolerate conspecifics. Russian hamsters form close, monogamous bonds with their mates, and if separated, they may become very depressed. This happens especially in males. Males will become inactive, eat more, and even show some behavioral changes similar to some types of depression in humans.<sup class="Template-Fact" style="white-space:nowrap;">[citation needed] This can even cause obesity in the hamster.

Chronobiology
Evidence conflicts as to whether hamsters are crepuscular or nocturnal. Khunen writes, "Hamsters are nocturnal rodents who [sic] are active during the night...",<sup class="reference" id="cite_ref-Kuhnen.2C_.282001.29_4-2">[5] but others have written that because hamsters live underground during most of the day, only leaving their burrows about an hour before sundown and then returning when it gets dark, their behavior is primarily crepuscular.<sup class="Template-Fact" style="white-space:nowrap;">[citation needed] Fritzsche indicated although some species have been observed to show more nocturnal activity than others, they are all primarily crepuscular.<sup class="reference" id="cite_ref-Fritz_3-2">[4]

Wild Syrian hamsters are true hibernators and allow their body temperature to fall close to ambient temperature (but not below 20°C). This kind of thermoregulation diminishes the metabolic rate to about 5% and helps the animal to considerably reduce the need for food during the winter.<sup class="reference" id="cite_ref-Kuhnen.2C_.282001.29_4-3">[5] Hamsters may not hibernate per se, but instead reduce the rate of a number of physiological systems, such as breathing and heart rate, for short periods of time. These periods of torpor (defined as "a state of mental or physical inactivity or insensibility"<sup class="reference" id="cite_ref-9">[10] ) can last up 10 days.<sup class="Template-Fact" style="white-space:nowrap;">[citation needed]

Burrowing behavior
All hamsters are excellent diggers, constructing burrows with one or more entrances, with galleries connected to chambers for nesting, food storage, and other activities.<sup class="reference" id="cite_ref-Fox_0-3">[1] They use their fore- and hindlegs, as well as their snouts and teeth, for digging. In the wild, the burrow buffers extreme ambient temperatures, offers relatively stable climatic conditions, and protects against predators. Syrian hamsters dig their burrows generally at a depth of 0.7 m.<sup class="reference" id="cite_ref-Gattermann_et_al..2C_.282001.29_10-0">[11] A burrow includes a steep entrance pipe (4–5 cm in diameter), a nesting and a hoarding chamber and a blind-ending branch for urination. Laboratory hamsters have not lost their ability to dig burrows; in fact, they will do this with great vigor and skill if they are provided with the appropriate substrate.<sup class="reference" id="cite_ref-Kuhnen.2C_.282001.29_4-4">[5]

Wild hamsters will also appropriate tunnels made by other mammals; the Djungarian hamster, for instance, uses paths and burrows of the pika.<sup class="Template-Fact" style="white-space:nowrap;">[citation needed]

Reproduction
A mother Syrian hamster with pups under one week old===Fertility=== Hamsters become fertile at different ages depending on their species. Both Syrian and Russian hamsters mature quickly and can begin reproducing at a young age (4–5 wk), whereas Chinese hamsters will usually begin reproducing at two to three months of age, and Roborovskis at three to four months of age. The female’s reproductive life lasts about 18 months, but male hamsters remain fertile much longer. Females are in estrus about every four days, which is indicated by a reddening of genital areas, a musky smell, and a hissing, squeaking vocalisation she will emit if she believes a male is nearby.<sup class="reference" id="cite_ref-Barrie_2-3">[3]

When seen from above, a sexually mature female hamster has a trim tail line; a male's tail line bulges on both sides. This might not be very visible in all species. Male hamsters typically have very large testes in relation to their body size. Before sexual maturity occurs, it is more difficult to determine a young hamster's sex. When examined, female hamsters have their anal and genital openings close together, whereas males have these two holes farther apart (the penis is usually withdrawn into the coat and thus appears as a hole or pink pimple).<sup class="reference" id="cite_ref-Barrie_2-4">[3]

Gestation and fecundity
Hamsters are seasonal breeders and will produce several litters a year with several pups in each litter. The breeding season is from April to October in the Northern Hemisphere, with two to five litters of one to 13 young being born after a gestation period of 16 to 23 days.<sup class="reference" id="cite_ref-Encyclop.C3.A6dia_Britannica_8-1">[9] Gestation lasts 16 to 18 days for Syrian hamsters, 18 to 21 days for Russian hamsters, 21 to 23 days for Chinese hamsters and 23 to 30 for Roborovski hamsters. The average litter size for Syrian hamsters is about seven pups, but can be as great as 24, which is the maximum number of pups that can be contained in the uterus. Campbell's dwarf hamsters tend to have four to eight pups in a litter, but can have up to 13. Djungarian hamsters tend to have slightly smaller litters, as do Chinese and Roborovski hamsters.

Intersexual aggression and cannibalism
Female Chinese and Syrian hamsters are known for being aggressive toward the male if kept together for too long after mating. In some cases, male hamsters can die after being attacked by the female. If breeding hamsters, separation of the pair after mating is recommended, or they will attack each other.

Female hamsters are also particularly sensitive to disturbances while giving birth, and may even eat their own young if they think they are in danger, although sometimes they are just carrying the pups in their cheek pouches.<sup class="reference" id="cite_ref-Fritz_3-3">[4] If captive female hamsters are left for extended periods (three weeks or more) with their litter, they may cannibalize the litter, so the litter must be removed by the time the young can feed and drink independently.

Weaning
An adult female and several juvenile dwarf hamsters (Phodopus sungorus) feedingHamsters are born hairless and blind in a nest the mother will have prepared in advance.<sup class="reference" id="cite_ref-Barrie_2-5">[3] After one week, they begin to explore outside the nest. They are completely weaned after three weeks, or four for Roborovski hamsters. Most breeders will sell the hamsters to shops when they are three to nine weeks old.

Longevity
Syrian hamsters typically live no more than two to three years in captivity, and less in the wild. Russian hamsters (Campbell's and Djungarian) live about two to four years in captivity, and Chinese hamsters 2.5-3.0 yr. The smaller Roborovski hamster often lives to three years in captivity.<sup class="reference" id="cite_ref-Fox_0-4">[1]

Hamsters as pets
A sable short-haired golden hamsterThe best-known species of hamster is the golden or Syrian hamster (Mesocricetus auratus), which is the type most commonly kept as pets. It is also sometimes called a "fancy" hamster. Pet stores also have taken to calling them "honey bears", "panda bears", "black bears", "European black bears", "polar bears", "teddy bears", and "Dalmatian", depending on their coloration.<sup class="reference" id="cite_ref-about.com_11-0">[12] Several variations, including long-haired varieties, grow hair several centimeters long and often require special care. British zoologist Leonard Goodwin claimed most hamsters kept in the United Kingdom were descended from the colony he introduced for medical research purposes during the Second World War.<sup class="reference" id="cite_ref-tel_12-0">[13] A Russian dwarf hamsterOther hamsters kept as pets are the various species of "dwarf hamster". Campbell's dwarf hamster (Phodopus campbelli) is the most common — they are also sometimes called "Russian dwarfs"; however, many hamsters are from Russia, so this ambiguous name does not distinguish them from other species appropriately. The coat of the Djungarian or winter-white Russian dwarf hamster (Phodopus sungorus) turns almost white during winter (when the hours of daylight decrease).<sup class="reference" id="cite_ref-Barrie_2-6">[3] The Roborovski hamster (Phodopus roborovskii) is extremely small and fast, making it difficult to keep as a pet.<sup class="reference" id="cite_ref-Fox_0-5">[1] The Chinese hamster (Cricetulus griseus), although not technically a true "dwarf hamster", is the only hamster with a prehensile tail (about 4 cm long)<sup class="Template-Fact" style="white-space:nowrap;">[citation needed] —most hamsters have very short, nonprehensile tails.

Many breeders also show their hamsters, so breed towards producing a good, healthy, show hamster with a view to keeping one or two themselves, so quality and temperament are of vital importance when planning the breeding.