Rats, mice, and relatives II

Hamsters (Cricetinae)

Class Mammalia

Order Rodentia

Suborder Sciurognathi

Family Muridae

Subfamily Cricetinae

Thumbnail description
Hamsters are mouse-like Old World rodents with chunky bodies; short, furry tails; and large cheek pouches, used to transport food; they have dexterous forepaws with four digits plus a "thumb knob"; hind feet have five digits; individual hamsters live alone in underground burrows, are active at night, and hibernate in winter

Size
2–13.4 in (5–34 cm); 0.9–31.7 oz (25–900 g)

Number of genera, species
7 genera; 18 species

Habitat
Deserts, dry plains, steppes, and cultivated fields

Conservation status
Endangered: 2 species; Vulnerable: 1 species; Lower Risk/Near Threatened: 4 species

Distribution
Throughout the Palearctic zone of Europe and Asia

Evolution and systematics

Members of the group Cricetinae appear in the European fossil record in the Middle Miocene (11.2 to 16.4 million years ago [mya]) and in the Asian fossil record in the late Miocene (6 to 11 mya). As of 2003, 15 extinct fossil genera have been documented.

Hamsters are related to voles, lemmings, and New World mice. In the mid-twentieth century, taxonomists split the group from the Muridae as a separate family, Cricetidae; however this split has been reversed.

The number of genera in Cricetinae is still debated. Some taxonomists place Calomyscus and/or Mystromys in this group; others place these two genera in their own subfamilies.

Some sources specify 18 species in 7 genera, while others describe 24 species in 5 genera. According to the Wilson and Reeder classification for 18 species in 7 genera, the rat-like hamsters, genus Cricetulus, include six Eurasian species; the golden hamsters, genus Mesocricetus, include four European and Middle Eastern species; the dwarf hamsters, genus Phodopus, include three Asian species; the Mongolian hamsters, genus Allocricetulus, include two Asian species; with the Cansumys genus having only one species, the Gansu hamster. Black-bellied hamsters are also the sole species in genus Cricetus, as well as the greater long-tailed hamster in genus Tscherskia.

Physical characteristics

Dwarf hamsters, genus Phodopus, are the smallest members of the group, averaging 2–4 in (5.3–10.2 cm) in length; the largest hamster is the black-bellied hamster, Cricetus cricetus, which at 7.9–13.4 in (20–34 cm) is about the size of a large rat or guinea pig.

Described as "all head and rump," hamsters have stout bodies and short legs and tails. The feet are wide, sometimes furry; the body fur is soft and thick and varies in color (depending on species) from gray to reddish brown; underparts can be white, gray, or black. Most hamsters have large cheek pouches.

Unusual for small mammals, the hamster stomach has two compartments; the forestomach, or cardiac stomach, has tough keratin as a structural component and is non-glandular, similar in structure and function to the rumen of cattle and other grazing animals. The second compartment—the pyloric, or glandular, region—is separated from the forestomach by muscular folds.

Hamsters have excellent hearing and an acute sense of smell; some species have scent glands on their flanks and use scent to mark their territories.

Distribution

The group is widely distributed in Eurasia, although a few species—the golden hamster is one example—have quite restricted

ranges. In the northern part of Eurasia, hamsters are found from central Europe through Siberia to northern China and Korea. In the south, various species occur from Syria to Pakistan.

Habitat

Most hamsters live in dry, open habitats such as desert borders, short-grass steppes, and rocky foothills, although the black-bellied hamster sometimes digs burrows along riverbanks. With the spread of agriculture, many species have moved into cultivated lands.

Behavior

Hamsters are active rodents with bodies well suited for running and digging. Most excavate their own burrows (some occupy burrows abandoned by—or still occupied by—other rodents). All are nocturnal and range far from their burrows at night to collect food that they carry home in large, internal cheek pouches. Inside the burrow, where special chambers are reserved for food storage, they stroke cheeks with paws to force the seeds out. In winter, hamsters hibernate if temperatures are sufficiently cold.

Some hamsters are gregarious, even highly social, while others tend to live alone or in pairs. Phodopus may be pairbonded; paternal care is unusual in hamsters and only Phodopus can be kept as mated pairs. Where burrows are closely spaced, this is only because appropriate habitat, soil loose and deep enough for digging, is in limited supply. Hamsters are fierce for their size and very aggressive to members of their own species. Pet golden hamsters must be maintained solitary. In addition to taking prey such as smaller rodents or baby birds the larger hamster species will attack humans and dogs when threatened.

Some species hibernate continuously, while others enter shallow daily torpor during the winter. In winter, rat-like hamsters do not hibernate continuously but awaken from time to time to eat stored food. Hibernation for uninterrupted periods of up to 28 days has been experimentally induced in the golden hamster through exposure to cold. The mouse-like hamster is active only at night during the summer, but it is also active by day in the autumn and winter.

Hamsters have a poor sense of sight despite their large protruding and round eyes. This is compensated by their well-developed sense of hearing that allows them to hear a wide range of sounds, including sounds in the ultrasonic frequencies,

which helps them communicate with each other without being heard by other animals. Hamsters also have an acute sense of smell and can distinguish one another by their distinct scents. Olfactory communication has been shown to play an intricate role in the daily activities of the golden hamster. Olfaction allows these nocturnal, burrowing, solitary, and territorial animals to communicate important individual information to one another and to receive information from their environment.

Feeding ecology and diet

Living in dry, comparatively unproductive habitats, hamsters often travel long distances in search of food. Besides carrying seeds and grain in their roomy cheek pouches, they carry large items such as root vegetables in their teeth. By storing food, hamsters make sure they will have enough to eat when food is in short supply—especially in winter.

Hamsters eat frequently throughout the day; their mixed diet is mostly seeds and grains but also includes green plant parts along with insects such as moths, beetle larvae, earth-worms,

and grasshoppers. Some hamsters kill smaller rodents, lizards, frogs, or baby birds, and they will eat carrion as well.

Reproductive biology

Hamster are sexually mature at a very young age, soon after they are weaned. Typically, males and females come together only to mate. The gestation period is quite short, ranging from 17 to 22 days. Litter size ranges from one to 16 pups with the average litter size around 11; females have eight to 17 nipples depending on species. In the wild hamsters may have two to four litters per year but species kept in captivity reproduce more frequently.

Hamsters are born hairless, with their eyes and ears closed and legs still somewhat undeveloped. The young do have teeth at birth, however, and eat solid food at seven to 10 days. They are weaned at 21 days.

Though most male hamsters play no role in raising the young, male Dzhungarian hamsters (Phodopus sungorus) are attentive fathers that assist at births, lick newborns clean, help keep them warm, and care for them when the female leaves the nest to feed. Like their mouse relatives, most hamsters live one to three years.

Conservation status

Threats to hamsters include loss of habitat, widespread use of rodenticides on farms, and, formerly, trapping for fur and as a pest-control measure. According to the IUCN Red List of 2002, two species are classified as Endangered: the golden hamster, Mesocricetus auratus of Syria, and the Hotson's mouse-like hamster, Calomyscus hotsoni of Pakistan. Four species are classified as Lower Risk/Near Threatened: the gray hamster, Cricetulus migratorius; the Afghan mouse-like hamster, Calomyscus mystax; Tsolov's mouse-like hamster, C. tsolovi; and the Urartsk mouse-like hamster, C. urartensis; one species is classified as Vulnerable, the Romanian hamster, Mesocricetus newtoni.

Significance to humans

Humans have long regarded hamsters as agricultural pests. Large species, particularly Cricetus cricetus, have been trapped for their fur; as recently as 2001, hamster fur made headlines as a controversial high-fashion item. Historically, farmers from China to Germany dug up hamster burrows to get at the stored grain—sometimes to feed farm animals, and sometimes—when times were hard—to feed themselves.

Since the twentieth century hamsters have been most important to humans as a biomedical research animal. Chinese hamsters were the first species to be used in laboratory research, in 1919. As of 2002, eight different species have been used in research on infectious diseases, cytogenetics, toxicology, and oncology, as well as obesity and diabetes, photoperiod changes, social behavior, and hibernation physiology. The species most widely used in research is the golden hamster.

Hamsters are also very popular pets; they are also bred for specialized colors and patterns, entered in shows, and exhibited at zoos.

Species accounts

List of Species

Black-bellied hamster

Cricetus cricetus

subfamily

Cricetinae

taxonomy

Cricetus cricetus (Linnaeus, 1758), Germany.

other common names

English: Common hamster, European hamster, field hamster.

physical characteristics

The largest hamster, 8–12 in (20–34 cm) long; males larger than females (10.5–12.5 in [27–32 cm] versus 8.7–9.8 in [22–25 cm]). Tail short and hairless, 1.6–2.4 in (40–60 mm). Weight 4.5–36.3 oz (112–908 g), averaging 18 oz (450 g) for males and 14 oz (350 g) for females. Thick fur is reddish brown above with white patches on the flanks, nose, cheeks, and throat, and black underparts—unusual in mammals. Color variations, from albino to melanistic, are common.

distribution

Black-bellied hamsters live in lowlands of central and Eastern Europe, from Belgium to the Altai region of Siberia.

habitat

Throughout much of their range, the hamsters' natural steppe habitat has been converted to agricultural land; they have adapted to living in and along farm fields, especially where both grain and root crops are grown. Occasionally, they dig burrows along riverbanks. These hamsters generally prefer low elevation habitat but can found up to an altitude of 2,000 ft (610 m).

behavior

When suitable burrowing sites are in short supply, black-bellied hamsters may burrow quite close together; however

these clusters are not true colonies; like most hamsters, members of this species are solitary in their habits. They are also active nocturnally and hibernate in winter. Winter burrows can be very deep, extending more than 6 ft (2 m) below the soil surface. Cricetus burrows are particularly complex, with several entrance tunnels, numerous chambers for nesting and food storage, and a dead-end tunnel used as a toilet area. The size of the burrow is correlated with the hamster's age; old females with young have the most complex burrows.

Black-bellied hamsters live in regions that can be quite cold in winter; they hibernate but wake up every 5–7 days to feed on their stored supplies. The length of hibernation is influenced by weather and other factors but typically occurs from the end of September through April.

When the hamster population in a given area reach a very high density, some members of the population become restless and leave, spreading out into new locations. Capable of swimming, the hamsters sometimes cross large rivers during these wanderings.

feeding ecology and diet

As with most hamsters the diet includes grains, beans, roots, and the green parts of plants; black-bellied hamsters also eat insect larvae—especially beetle larvae—frogs, earthworms, and field mice. They often store very large quantities of cereal grains, seeds, peas and potatoes in their winter burrows; there are reports of burrows containing as much as 198 lb (90 kg) of food.

reproductive biology

Most breeding activity takes place between June and August, although breeding can begin earlier or continue later, depending on location and climate. Probably serially monogomous. A courting male will enter the female's territory and mark the area with secretions from glands in his flanks. A lengthy courtship ritual ensues, in which the male runs after the female, making a loud sniffing noise that serves as his mating call. After mating occurs, the female becomes aggressive and drives the male away. (In captivity, however, male black-bellied hamsters sometimes help to raise the young.)

The female cushions the floor of the nest chamber with grass stalks. The gestation period is 18–20 days. A typical litter is 4–12 pups; the female has eight nipples and usually raise no more than eight young. Newborns weigh about 0.2 oz (7g). They start to eat solid food at one week, when their eyes are still closed; at age two weeks they open their eyes and have acquired a full coat of fur. At three weeks they are weaned; they will reach adult size at eight weeks. A female typically has two litters per year in the wild. These are comparatively long-lived hamsters, sometimes reaching the age of eight years old.

conservation status

Sometimes considered a serious pest on farms, black-bellied hamsters in the twentieth century were often systematically poisoned with rodenticides. This practice, combined with habitat loss, due both to changes in farming practices and spreading industrial construction, has led serious population declines in some locations. As of 2000, this hamster was protected under the European Community Habitats Directive as a threatened species in Germany, Belgium, the Netherlands, France, and Austria. They are also protected in Bulgaria, Croatia, and Slovenia, where they are uncommon, not because of human actions, but because they are at the edge of their range.

significance to humans

As land was increasingly cleared for farming in the Middle Ages, this probably created conditions favorable for hamsters and led to a rise in populations. Historically this species has been widely hunted for food and trapped for its colorful fur, which was used to make clothing or as a warm lining; as of 2001 hamsters were still being trapped in eastern European nations where they are common, such as Hungary, and the fur was still being used in some high-fashion garments.

Black-bellied hamsters have historically been a particular pest in corn fields; corn is often the last crop to be harvested, so hamsters from neighboring fields congregate in corn fields after their other food sources are gone. It's worth noting that this species can also be helpful to farmers because it hunts field mice and insect pests.

Finally, the black-bellied hamster is sometimes used as a lab animal, particularly in oncology research.

Golden hamster

Mesocricetus auratus

subfamily

Cricetinae

taxonomy

Mesocricetus auratus (Waterhouse, 1839), Aleppo, Syria.

other common names

English: Syrian hamster; Syrian golden hamster.

physical characteristics

Medium sized, about 6–7 in (15–18 cm) long, stubby white or pink tail is 1.2 cm (0.5 in); weight 3–4 oz (90–120 g), with females larger than males. Fur is light reddish brown to golden with white or cream-colored underparts; domesticated animals have been bred for a wide variety of colors, patterns, and fur textures. Cheek pouches are very large, extending back behind the shoulders. Females have 12–17 nipples. Life span is 2–3 years.

distribution

Although some accounts assert that this species is extinct in the wild, it may in fact be locally common; specimens were collected in the Mount Aleppo region, in northwestern Syria in 1999; other specimens were sighted near Jarablus in Syria in 1986 and near Gaziantep in Turkey, mostly recently in 1999.

habitat

Historically, this hamster's native habitat has been described as dry, rocky steppe or brushy slopes. The wild population discovered in 1999 was living in agricultural fields planted with annual crops including barley, chickpeas, lentil, melons, tomatoes, and others; hamsters were most often found on plots of legumes. Burrows were also found on the embankments around irrigation wells; all of the burrows were in sandy clay soil overlaying limestone bedrock.

behavior

Though mostly nocturnal, golden hamsters are sometimes active in daytime. Burrow depths measured on the 1999 expedition ranged from 14 to 41.3 in (36 to 106 cm), averaging about 25.4 in (65 cm). Burrow entrances averaged 1.6–2.0 in (4–5 cm) in diameter and led to vertical entrance tunnels. Occupied burrows had their entrances plugged with lumps of earth slightly below the soil surface. Nest chambers ranged from 2.9–7.8 in (10–20 cm) wide; the spherical nests were made of dry plant materials. In contrast to black-bellied hamster burrows, which are complex and often have more than 10 branches, a golden hamster's burrow is relatively simple, with few side tunnels. This species reserves a blind-end tunnel for urination but defecates throughout the burrow. They are thought to hibernate in winter from November to February, although the hibernation state is not total. In the lab, hibernation can be induced at temperatures below 46°F (8°C). Predators are uncommon in the are where these hamsters occur (because of the dense human population) but in 1999 hamster remains were found in a barn owl pellet.

feeding ecology and diet

Although lab diets have been carefully worked out, very little is known about how these hamsters live in the wild.

reproductive biology

In the wild the breeding season is thought to begin in February (lab animals breed year round). Males and females meet only to breed and the males do not assist in rearing the young. The female's estrous cycle is four days long and estrus lasts 27.4 hours. After conception the gestation period is usually 16 (but sometimes up to 19) days. The litter size can range from one to 16 pups; litters of six to nine are typical. The pups are blind and hairless at birth and typically weigh 0.07–0.1 oz (2–3 g); they grow quickly, are weaned by 20 days, and are sexually mature and ready to breed at 7–8 weeks old. If she feels threatened, the mother may transport her young in her cheek pouches (this occurs only during their first three days of life).

conservation status

This species is listed as Endangered.

significance to humans

Among endangered species, golden hamsters are unusual in that humans may have helped to prevent the species from becoming extinct by taking animals from the wild to use in biomedical research. The story begins in 1930, when four juvenile animals were taken from a burrow in a Syrian wheat field in 1930 and brought to the Microbiological Institute of Jerusalem, with the goal of using them instead of Chinese hamsters, which had failed to breed in captivity in a study of the disease Leishmaniasis. The golden hamsters reproduced very well in captivity; their descendents, along with the descendents of another 12 animals collected in 1971, have been distributed to research institutions all over the world. Although as of 2003, eight hamster species are used in research, golden hamsters are by far the most the most common experimental subject; in addition, they are the most popular of all the hamster species kept as pets. Escaped pets have established wild populations in some locations in the British Isles.

Despite their endangered status, in Syria the remnant wild populations are still considered as pests and trapped or poisoned using rodenticides provided by the government. Farming practices are another problem. In May and June fields are harvested, then burned or ploughed under; meanwhile sheep are turned out to graze in any remaining fields. At this time it may be hard of hamsters to find cover, nutrition, or the extra food they need to store for the winter.

Resources

Books

Baumgart, G. "The European Hamster. Cricetus cricetus L. (1758) in Alsace. 1. Ancient and Recent Data (1546–1995), 2. Hypotheses on the Cause of its Extinction." Gerstheim, France: Report of the National Office of Hunting 1967.

Nowak, Ronald M. Walker's Mammals of the World. Vol. 2, 6th ed. Baltimore: Johns Hopkins University Press, 1999.

Subcommittee on Laboratory Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council. Nutrient Requirements of Laboratory Animals. Fourth Revised Edition. Washington, DC: The National Academy of Sciences, 1995.

Van Hoosier, G. L., Jr., and Charles W. McPherson. Laboratory Hamsters. New York: Academic Press, 1987.

Periodicals

Gattermann, R., et al. "Notes on the Current Distribution and the Ecology of Wild Golden Hamsters (Mesocricetus auratus)." Journal of Zoology 254, no. 3 (2001): 359–365.

Nechay, Gabor. "Status of Hamsters Cricetus cricetus, Cricetus migratorius, Mesocicretus newtoni and Other Hamster Species in Europe." Nature and Environment 106 (200): 1–73.

Cynthia Ann Berger, MS