Primarily nocturnal (2) or crepuscular (1), the sika deer can also sometimes be seen foraging during the day, grazing singly or in small herds (1) (2). The sika deer is not a particularly gregarious species, and adult males tend to be solitary for most of the year (2) (3), only gathering together once their antlers have been shed (2). Male and female sika deer occupy different areas for most of the year, and only come together during the mating season (3). Sika deer do not migrate large distances between summer and winter (6), but this species is known to migrate to lower valleys in the winter (1). Interestingly, the sika deer is a good swimmer, and is also capable of jumping over objects up to 1.7 metres in height (2).
The sika deer is a herbivorous species (6), feeding on many different plants (2) including grasses, browse and even fruit (1). In the summer, this species’ diet tends to consist primarily of grasses and herbs, whereas in winter months more woody plants are consumed (2). The shoots and bark of coniferous trees may sometimes be taken (3), and the sika deer has been reported to feed on crops in the spring and early summer (2).
As in other deer, male sika deer rub their antlers against trees both to remove velvet and as a territory marker (5). The antlers are cast in May (2) (5), and grow throughout the summer (5). The breeding season of the sika deer, known as the rut, typically occurs in the autumn (1) (4), from about September to November (3) (6) or December (2). Males establish and defend territories (3) (4), using their forefeet and antlers to dig holes up to 1.6 metres wide and 0.3 metres deep in which they frequently urinate to signal territory boundaries (2). Fierce fighting often occurs between rival males (2) (4), who all try to drive available females into their territories where mating takes place (2). Successful male sika deer may mate with as many as 12 females, and may be so intent on finding females that they do not feed until later on in the rutting season (2).
The gestation period of the sika deer is around 30 weeks (1) (2) (3) (4) (6), after which time the female gives birth to a single calf (2) (3) (4) (6), rarely two (3) (6). The timing of birth varies slightly with geographic location, but young are typically born between April and July (1), mostly in May and June (2) (3) (6). Young sika deer grow rapidly, and are weaned by late summer (4), approaching the weight of the mother by eight months of age (2). Female sika deer may be sexually mature at six months of age, and tend to first breed as yearlings (2) (6).
The sika deer has been reported to live for up to 12 years in the wild (2), but individuals in captivity have been known to reach 25 years old (1) (2).