the gestation period is about nine months, roughly around 280 days, after which a single offspring is usually born; twins are born rarely. the gestation period is significantly longer than any other deer besides the roe deer. père david's deer are considered seasonal breeders because three out of four calves are born during april in captive european populations. the breeding season is 160 days with the mating season usually being in june and july. calf weight, calculated using robbins and robbins equation, tends to be between 11.3 and 13.2 kg. the juveniles (referred to as either "fawns" or "calves") have a spotted coat, as is commonly seen in most species of deer. they are known to develop very quickly after birth. they reach sexual maturity at about 14 months. the average lifespan of a père david deer is up to 18 years.