is highly varied. In 1968, the first four examples of the hamster were caught in Western Siberia and brought to the Max Planck Institute in Germany. Pet ownership The hamsters are often found on the pet market in Europe, Japan, and North America. Care of the hamster is similar to all other species of Phodopus. The hamsters, along with most rodents, are prone to tumours. They can also receive injury in the cheek pouch by sharp objects damaging the fragile inner lining. Other health problems include bite wounds, broken teeth, constipation, dehydration, dental malocclusion, diarrhea, and ear problems. Breeding Winter white dwarf hamsters reproduce at a faster rate than Syrian hamsters. Phodopus species are able to become pregnant again on the same day that they have given birth. This can all happen within a 36-day period. This is done as a survival strategy to produce large numbers of offspring in a short period of time. This places tremendous demands on the mother. Research suggests biparental care in Campbell's hamsters (P. campbelli) but not in winter white hamsters (P. sungorus). Frequent fighting can occur between the pups and as soon as they are weaned from their mother, they are separated from her. Most of the dwarf hamsters grow to 3 to 4" long. Hamsters maintained indoors that get artificial illumination during autumn and winter are likely to breed all year round, whereas in the wild and in animals maintained in captivity but under entirely natural light-dark cycles, breeding is restricted to the long days of spring and summer. During the breeding time, the hamster may become aggressive. After mating, the female may want to attack the male to protect her babies. The male usually hides in holes or caves to escape the vicious bite of the female. The hamster's estrous cycle lasts four days; every four days, the female may accept the male back to breed again. This usually occurs when the darkness of the evening sets in. If male and female hamsters are not housed together from a young age, determining if the female is willing to breed with the male is difficult. Hybrids Of the five species of hamsters kept commonly as pets, only Campbell's dwarf hamster and the winter white dwarf hamster are able to interbreed and produce live hybrid offspring. Although hybrids make suitable pets, the breeding of hybrids and cloning can cause health and reproduction problems.