Rusa deer are distinguished by their large ears, the light tufts of hair above the eyebrows, and antlers that appear large relative to the body size. Their coat is grayish-brown and often appears coarse. Unlike most other deer species, newborn fawns do not bear spots. The antlers of these deer are lyre-shaped and three-tined. Male Rusa deer are bigger than females.
Rusa deer are native to the islands of Java, Bali, and Timor in Indonesia. They have been introduced to Irian Jaya, Borneo (Kalimantan), the Lesser Sunda Islands, Maluku, Sulawesi, Pohnpei, Mauritius, Fiji, Tonga, Samoa, Vanuatu, the Solomon Islands, the Christmas Islands, the Cocos Islands, Nauru, Australia, New Caledonia, New Zealand, Papua New Guinea, New Britain, and New Ireland. Rusa deer inhabit open dry and mixed deciduous forests, parklands, savannas, mountains, shrublands, and marshes.
Rusa deer are active mostly in the early morning and late afternoon. They are rarely seen in the open and are very difficult to approach due to their keen senses and cautious instincts. These deer are very sociable, and individuals are rarely found alone. Males and females live separately most of the year and come together only during the mating season. When alarmed, the male produces an extremely loud honk. This is an alarm call and alerts any other deer in the vicinity.
Rusa deer are polygynous which means that males mate with more than one females during each breeding season. They breed in July and August. During this time, males decorate their antlers with grass and twigs to attract females and intimidate competitors. Males become very vocal and contest by calling in a loud, shrill bark and dueling with the antlers. The female gives birth to one or two fawns after a gestation period of 8 months, at the start of spring. Fawns stay with their mother and are weaned at 6-8 months after birth. They reach reproductive maturity at 3-5 years, depending on habitat conditions.
Rusa deer are threatened by habitat destruction, illegal hunting and also by expansion of agriculture on Java. These deer are poached with guns, snares, and dogs. Ruse deer are hunted in their native range for meat, medicinal products, handicrafts products, and, locally, pets.
According to the IUCN Red List, the total native population size of Rusa deer is fewer than 10,000 mature individuals. There are estimated populations of this species outside its native range: New Caledonia - 120,000 deer; Mauritius - 60,000 deer; Wasur National Park, Indonesia - over 8,000 deer; New South Wales, Australia - 5,000 to 10,000 deer; Victoria, New South Wales, and Queensland - less than 100 deer. Currently, Rusa deer are classified as Vulnerable (VU) on the IUCN Red List and their numbers today are decreasing.