The pregnancy, or gestation period, for Sumatran rhinoceroses is relatively long, lasting about 15 to 16 months. This extended period is one of the factors contributing to the challenges they face in terms of reproduction and population growth, as it limits the number of offspring a female can produce in her lifetime. The birth of a Sumatran rhinoceros calf can occur at various times throughout the year, as there is no specific mating season for this species.