Originally the preferred habitat in Japan was large forests with clearings, but they have adjusted well to the cultivated man-made landscapes. Since many sika deer live in a semi-tame state in parks and on farms, they are easily introduced into other countries, especially since the northern subspecies does well in the climate of Europe. In addition to European forests and parks, they now also inhabit the island of Madagascar. Presently in Germany, there are several populations living in the wild. Grazers who occasionally browse, eat flowers and fruit.
Sika deer are gregarious, travelling in herds.
They are normally diurnal. The rut of the northern subspecies is in November and December. The males then cry with high notes which often change into piercing sounds. The females' gestation period is seven and a half months, and the young are born by the end of June to the beginning of August. Usually only one young is born, although twins occur on occasion.