About Phodopus sungorus (Pallas, 1773)
This description covers the physical characteristics of the winter white dwarf hamster, Phodopus sungorus. Its coat is less woolly than the coat of Campbell's dwarf hamster. Along with its natural standard coloration, winter white dwarf hamsters can also have sapphire, sapphire pearl, or normal pearl color patterns. Their head and body length measures 70–90 mm, their tail length measures 5–15 mm, and their hind legs measure 11–15 mm. Body weight changes dramatically across the year, and reaches its lowest point during winter. In males, body weight ranges from 19 to 45 grams (0.67 to 1.59 oz), while in females it ranges from 19 to 36 grams (0.67 to 1.27 oz). Individuals kept in human care are slightly heavier than wild counterparts. The average lifespan of the winter white dwarf hamster is one to three years in captivity, though some captive individuals may live longer. In the wild, this species is known to live as little as one year. In summer, the fur on the back of the winter white hamster changes from ash-grey to dark brown, or sometimes takes on a pale brown tint. The face becomes grey or brown, while the mouth area, whisker area, and ears are slightly lighter. The outer edges of the ears and the rims of the eyes have black edges. The rest of the head is dark brown or black. A black-brown dorsal stripe runs from the head down to the tail. The throat, belly, tail, and limbs are white. The ears are grey with a pinkish tint, with scattered black hairs. Hairs on the underside are completely white. The light-colored coat of the underside extends upward onto the shoulders, flanks, and hips in three upward-curving arches. These upward arches form three curved lines that separate the light underside fur from the darker black-brown fur of the upper body. In addition to its typical natural coloration, winter white dwarf hamsters can also have pearl, sapphire, sapphire pearl, and marbled colorations. Other color variants exist, but these are strongly suspected to only appear in hybrid crosses between winter white dwarf hamsters and Campbell's dwarf hamsters. These less common, hybrid-associated colorations include mandarin, blue, argente, yellow blue fawn, camel, brown, cream, merle, and umbrous. In winter, the fur becomes more dense, and sometimes develops a grey tint on the head. More than 10% of captive winter white dwarf hamsters retain their summer coat through their first winter. By their second winter, only a small number of individuals will change into a full winter coat, and winter coloration becomes less pronounced. Moulting into winter fur starts in October or November and finishes in December. Moulting into summer fur starts in January or February and finishes in March or early April. Moulting, whether for summer or winter fur, begins on the head and along the back spine, then progresses outward to the sides, legs, and underside. Summer hairs grow longer, reaching approximately ten millimetres in length. Hair pigmentation is controlled by the hormone prolactin and color genetics. A day length of less than 14 hours is required to initiate the change to winter coat. Some evidence suggests these hamsters can sense directional changes in photoperiod length: one experiment found that a transition from 16 hours of light to 14 hours is enough to initiate a shift to winter coat. A change to winter coat can even be triggered in summer by exposure to short day lengths. The shift back to summer coat occurs in autumn, when day length changes again. Captive hamsters kept at constant indoor temperatures start these seasonal coat changes later, and their winter coloration is less pronounced. The eyes of the winter white hamster are black, unless the individual is albino, in which case the eyes are red.
