18.

Common Hamster

Cricetus cricetus

French: Hamster d'Europe / German: Feldhamster / Spanish: Hamster comun

Other common names: Black-bellied Hamster, European Hamster, German Marmot (archaic), Great Hamster

Taxonomy. Mus cricetus Linnaeus, 1758, «“ Habitat.. in Germania. [= Germany]. ”»

Nine subspecies of C. cricetus were recognized in the past, but that number grossly exaggerated and obscured actual patterns of geographic variation. Phylogeographical architecture is largely the outcome of the Last Glacial Maximum, and estimated times of divergence among phylogroups vary between 10,000 and 150,000 years. Greatest genetic and morphological diversity occurs in the western segment of the distribution. Populations occurring east of the Carpathian Mountains are rather uniform, containing a single phylogeographical line. There is no agreement over the recognition of subspecies. Monotypic.

Distribution. From W Europe E to the River Yenisei in Siberia, including Belgium, Netherlands, France, Germany, Poland, Czech Republic, E Austria, Slovakia, Hungary, Slovenia, N Croatia, N Serbia, Romania, N Bulgaria, Moldova, S Belarus, Ukraine, Russia, Kazakhstan, and NW China (Xinjiang).

Descriptive notes. Head-body 175-320 mm (males) and 165-270 mm (females), tail 33-68 mm (males) and 27-68 mm (females); weight 158-860 g (males) and 146-600 g (females). Male Common Hamsters are on average 24% heavier than females. Size varies among regions but with no obvious trend. Differences were also reported at centennial and millennial time scales. The Common Hamster is the largest and most colorful member of the subfamily Cricetinae . General form is heavy with short feet and tail, moderately large eyes and long rounded ears. There are five palmar and six plantar pads. Expandable inner cheek pouches extend backward to shoulders. Females have two pairs of inguinal and pectoral nipples (i.e. eight teats). Pelage is tricolored, with brownish buff upper parts, black belly, and contrasting light patches between brown and black areas. From anterior to posterior, light patches occur on cheeks, neck, axillary, and thighs. About 13% of Common Hamsters lack thigh patches, and very exceptionally all light patches are absent. White cuff of variable size occurs on front feet. Wide range of color variants have been reported. Variants are more diverse and more frequent in Europe than Asia. Common Hamsters in the west are characterized by a large white chest spot that is small and rarely present in the east; e.g. only 1-1% of Common Hamsters from Asia display a chest patch that is always small and frequently diffused. White chin streak is also larger and more frequently present in the west. Color variants include black, piebald, bicolored, white, albino, yellow (flavistic), red, sand, and iron-gray. These variants are rare, occurring in Central Europe at frequencies between less than 0-1% and 0-3-1%. Proportions of black hamsters can be more abundant locally; e.g. up to 50% in Thuringia (Germany) and more than 80% in Ukraine and Bashkortostan (Russia). Frequencies of black hamsters vary among years and also depend on population make-up. In the past, the Common Hamster was frequently regarded as dimorphic, with tricolored and black morphs. Black morph, however, contains a variety of dark and black variants. Standard tricolored pattern grades into the truly melanistic extreme through a gradation in darkening. Skull is heavily built, with powerful supratemporal ridges and widely bowed zygomatic arches. Rostrum is heavy and wide, diastema is long, and auditory bullae are small and oval. Mandible is shallow, ramusis low, and processes are powerful. Molars are low-crowned and cuspidate, with cusps arranged in two parallel rows.

Habitat. Steppe and forest steppe zones. Common Hamsters penetrate into boreal forests in the north and semi-deserts in the south. Borders are set by isotherms of 17°C in the warmest month (in the north) and 2°C in the coldest month (in the south). Western part of the distribution is largely in the deciduous forest zone. Open landscapes are preferred, with soil layer more than 1 m deep and relatively low groundwater levels. Heavy loamy and clayey soils are optimal. Common Hamsters prefer lowlands at elevations below 400 m and low mountains up to ¢.1500 m. Highest elevational records are on Tarbagatai and Dzungarian Alatau at 2000-2200 m. Common Hamsters occur in anthropogenic habitats (fields, gardens, orchards, and embankments) throughout their distribution and prefer the most productive agricultural areas. Perennial crops and mixtures of grasses and legumes are the most suitable because of continuous food availability and lower disturbance than in fields of cereal crops. They occupy meadows and fallow land at low densities. In Asia, they also live in open woodland, alder ( Alnus, Betulaceae) gallery forests, birch ( Betula, Betulaceae) stands, secondary pine ( Pinaceae) and birch forest, mixed forests, and bushland. They enter haystacks, stables, and buildings in fields and villages. In the 20" century, a process of adaptation to urban environments became increasingly more evident. It was perhaps triggered by food availability in urban areas and reduced pressure from predators. Records of urban Common Hamsters date back to late 19" century (Moscow) and became more common since the 1970s. They are now present in parks, gardens, cemeteries, and embankments of many towns and cities between Germany and Russia. In Vienna, Lublin, Nalchik, and Simferopol, Common Hamsters have penetrated urban areas where they were not known previously and have established truly urban populations.

Food and Feeding. Common Hamsters are herbivorous and omnivorous, but they are catholic and opportunistic and promptly adaptto local conditions. Mean daily consumption per individual is 48-8 g of grain and 71-8 g of tubers. When extrapolated to entire season, consumption is 10 kg of seeds and 15 kg of tubers. Main foods include green plants, tubers, and seeds, occasionally complemented with invertebrates (earthworms, snails, and insect larvae and adults) and small vertebrates (frogs, lizards, ground-nesting birds, and rodents). In Poland, 82% of stomachs contained vegetable matter (green plants in 74%) and 13% contained animal food. Green plants were important from spring to autumn, grains were staple food in summer and autumn, and roots and tubers in autumn. Animals were minor dietary components: beetles (8:5% of stomachs), slugs ( Limacidae; 3-9%), hymenopterans (1:3%), small mammals (1-8%), and caterpillars (0-6%). It is estimated that diets contain 10-13% protein. Canibalism was reported at high densities. During a population peak in Slovakia, 5-3-9-9% of stomachs contained remnants of conspecifics. Clover ( Trifolium, Fabaceae), plantain ( Plantago, Plantaginaceae), and dandelion ( Taraxacum, Asteraceae) are the most important dietary plants. Common Hamsters feed on fruits and seeds where available (e.g. chestnut, plum, walnut, oaks, maple, pear, apple, cherry, and almond). In addition to aboveground feeding, Common Hamsters also cache food. Males spend ¢.80% of the time actually feeding; females spend 96% of the time caching food and foraging afterward inside the burrow. Food is carried into burrows in cheek pouches that can carry 50 g. Most reports on caches are from autumn; they contain cereal grains, vegetables, tubers and roots (potatoes and beets), alfalfa, and dandelions. Caches are usually 2-3 kg, and 1.1-5 kg is the minimum for successful hibernation. Caches containing up to 65 kg were also reported.

Breeding. The Common Hamster is polygynous; males frequently change their burrows in search of estrous females. Reproductive period lasts from April (rarely March) to August (rarely September); testes start regressing in July-August. Ovarian activity is initiated in hibernaculum, and most females emerge from hibernation with open vagina. Gestation lasts 17-17-5 days, and birth is followed by a postpartum estrus. Next gestation usually coincides with lactation and is prolonged to 18-37 days. On average, a female can have 1-2 litters/season; third litter is rare. A captive female delivered ten young in ¢.40 minutes. Numbers of embryos are 4-21 (means 8-1-13-2). Captive litters have 4-12 young (means 4-4-7-8), and wild-born nests contain 3-15 young older than two weeks (means 8-1-8-6). Largerlitters were reported from Russia, with means ranging from 17-4 young for the first litter to 13 young for the third litter. Mean litter size might increase from west to east, and possible continuous declines have occurred since 1950. Young are born naked, blind, and with sealed ears, and they already have claws, vibrissae, and incisors. They are 50-52 mm long and weight 4-8-5-8 g. White spots become visible and ears unfold on day 2, meatus opens on days 13-15, and eyes on days 14-16. One-month-old young have an adult appearance. They start leaving burrows at c.3 weeks of age and are weaned at 3-5 weeks, at which time, sexual differences in size become apparent. Females can reproduce in their first year at weights of 210-280 g. They willingly adopt young from alien litters. On average, males live 11-5 months and females live 15 months. Maximum live expectancy is 2-2 for males and 2-4 years for females; comparative values for captive hamsters are four and five years. Main sources of mortality are hibernation and predation. Population numbers oscillate with mass outbreaks every 8-11 years; peak densities can reach up to 300 ind/ha.

Activity patterns. Common Hamsters are nocturnal and crepuscular, but during breeding season and when building winter caches, activity is around the clock. They hibernate for 180-210 days (e.g. in south-western Siberia and Kazakhstan) and show considerable variation in length of torpor bouts. Adult males dig winter burrows in summer, cache food, and enter hibernacula in late August. Adult females follow in September and young individuals in October. Before entering hibernacula, adult males have more body fat than adult females, and juveniles have less body fat than adults. During hibernation, Common Hamsters sit partly erect on hindlegs. Body temperatures drop from 37-8-39-3°C in euthermic individuals to 4-7-5°C, and respiration is reduced to 2-13 breaths/ minute. Postimmergence euthermy lasts 10-72 days when individuals depend on stored food. Males have more torpor bouts than females and hibernate 82% of the time in hibernacula; females are euthermic for 48% of the time. During hibernation, adults loose proportionally more weight (12:2%) than juveniles (4-2%). If an individual runs short of cached food, it may leave a burrow even at ambient temperatures below —20°C. Individuals dwelling in human settlments can stay active throughout winter and feed on stored food. The Common Hamster is a good digger and excavates elaborate burrow systems. Each individual has its own burrow. Diameters of tunnels are 5.9-5 cm (average 7-6 cm). Average amount of unearthed soil is 29-9 kg/burrow, and recorded maximum was 300 kg. Hamsters usually have summer and winter burrows. Breeding burrows are elaborate, with 1-5 oblique passages and 1-2 vertical entrances. Vertical tunnels are dug from the inside, and soil is removed through oblique passages. Total lengths of tunnels are 154-380 cm. Tunnels lead to 1-4 (usually 2) nesting chambers (mean dimensions 36 x 21 cm and 16-76 cm deep). They contain soft plant material, mainly grasses. Each burrow system has 1-8 latrines that are frequently short dead-end tunnels. Distances between female burrows are 15-20 m in the Altai Republic and 30-50 m in western Siberia. Summer burrows of males are simpler and more widely scattered. They have 45-227 cm of tunnels and a nest chamber (mean dimensions 27 x 23 cm and 40-45 cm deep). Burrows of young individuals are similar to those of males; i.e. lengths of tunnels are 44-160 cm and nest chamber (23 x 17 cm) is 30-35 cm deep. Winter burrows are more complex, with 1-4 oblique tunnels measuring 30-125 cm and 1-4 vertical passages measuring 27-70 cm. Total lengths of tunnels are 4-5 m, and maximum reported length is 26-2 m. Tunnels lead to a nesting chamber (35 x 22 cm) and 1-7 caches (42 x 24 cm) located around the nest. Female burrows are less complex, and total lengths of tunnels are shorter (2:5-3 m). Burrows of young individuals are the most simple, with c.1-5 m tunnels. After hibernation ends in March-April, 3-5-50% of Common Hamsters reoccupy their summer burrows. Distances between winter and summer burrows are 0-3-0-5 km in the Altai Republic and up to 2 km in the Volga region; average distance is 373 m for adult females and 800 m for adult males. Common Hamsters also excavate short (30-80 cm) emergency shelters 5-100 m away from main burrows. Females usually have 1-4 shelters/ main burrow. In emergencies, individuals might escape into natural shelters; e.g. into a burrow of a Eurpoean Ground Squirrel (Spermophillus citellus) or under a rock.

Movements, Home range and Social organization. At night, Common Hamsters move 200-2500 m from burrows but only 40-50 m during the day . Females are more philopatric and have smaller home ranges than males. Mean movements of adults between two consecutive captures were 35-7 m for females and 94-6 m for males; corresponding values for subadults were 35-7 m for females and 94-6 m for males. Feeding radius is ¢.30 m around the burrow, but distances of 400-700 m are crossed to reach patches with preferred food. When hoarding food for winter, Common Hamsters can move distances up to 1-2-5 km from burrows. Males have exclusive territories (surface area of 0-5-2 ha) that are scent-marked using flank and tarsal glands. Home ranges of females are smaller (0-1-0-6 ha) and widely overlap. Ranges of breeding females are only 425-600 m*. Weaned young occupy ranges of 0-21 ha (females) and 0-25 ha (males). During postnatal dispersion, individuals hamsters move 2-3 km; longest distance was 5-6 km by a male. Common Hamsters are fearless and aggressive. During antagonistic encounters, they chatter teeth and inflate cheek pouches.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Although severe population declines and local extirpations of Common Hamsters were known at the time ofthis clasification, the status was justified by stable populationsin the eastern part of the distribution. Hence, the overall decline did not approach the threshold of 30% over ten years (or three generations) needed to qualify as Vulnerable. Subsequently, a decline also became apparent in the east, specifically in Poland, Ukraine, and parts of western Russia, suggetsing that conservation status needs to be reassessed. The Common Hamster was killed extensively in the past as an agricultural pest and forits pelts. In the 1960s, more than one million Common Hamsters were killed annually in the Saxony-Anhalt region of Germany. Changes in agricultural land use, specifically weed-free largescale crops, simplification of rotations, improved harvesting techniques leaving no food on the ground, early tillage, and deep ploughing, have been detrimental to Common Hamsters. Populations on the western edge of the distribution were the most affected. Populations in Belgium, France (where restricted to Alsace), and Netherlands survived thanks to conservation efforts that included “hamsterfriendly management” and, in extreme cases, captive breeding and restocking of wild populations.

Bibliography. Banaszek et al. (2010), Berdyugin & Bolshakov (1998), Feoktistova, Surov et al. (2013), Gershenson (1945), Grulich (1981, 1987), Hell et al. (2005), Holisova (1977), Kayser & Stubbe (2000), Krystufek, Pozdnyakov et al. (2016), Krystufek, Vohralik et al. (2016), Millesi et al. (2008), Neumann et al. (2005), Niethammer (1982a), O'Brien (2015), Popov (1960), Schroder et al. (2014), Siutz, Franceschini & Millesi (2016), Siutz, Pluch et al. (2012), Stefen (2013), Surov et al. (2016), Vohralik (1974, 1975), Weinhold (2008).