A minimum of 51 tamarao (Bubalus mindorensis) occurred in a 20-km2 study area at the Mt. Iglit Game Refuge and Bird Sanctuary, Occidental Mindoro, the Philippines. Juvenile bull tamarao formed groups similar to those in juvenile water buffalo (Bubalus bubalis), but adult tamarao did not form clans or aggregations like buffalo. THE TAMARAO WAS KNOWN long before it was described (Heude 1888, Steere 1888), but it frequently was confused with the anoa (Bubalus [Anoaj depressicornis, Bubalus IIAnoa1 quarlesi) (Everett 1878). Taxonomists now agree that the tamarao is a member of the genus Bubalus, but Bohlken (1958) considered it a subspecies of the water buffalo, and Groves (1969) more recently accorded it specific status. Although tamarao occurred on Luzon during the Pleistocene (Beyer 1957), during historic times they have been restricted to the island of Mindoro in the Philippines. Tamarao have been legally protected since 1936, but Harper (1945) warned that the species faced early extinction primarily due to habitat destruction and poaching. Numbering perhaps 10,000 in 1900 (Harrisson 1969a), the tamarao population decreased to about 1000 in 1949 and 244 in 1953 (Manuel 1957). By 1969 only 100 tamarao were believed to inhabit four regions in Mindoro (Harrisson 1969b, Alvarez 1970). The 90-km2 Mt. Iglit Game Refuge and Bird Sanctuary was established in one of the four Mindoro regions in 1961 and was enlarged to 755 km2 in 1969. Talbot and Talbot (1966) estimated a minimum of 17 tamarao survived at Mt. Iglit in 1964; five years later Harrisson (1969b) estimated at least 20 remained. This paper offers criteria for estimating the age of tamarao in the field, documents population characteristics of tamarao on a 20-km2 study area at Mt. Iglit, and compares the behavior of tamarao, whose range was heavily forested before human arrival (Landicho 1952, Wernstedt & Spencer 1967), with that of the water buffalo, which is adapted to more open habitat (Halder 1973). STUDY AREA The study area lies in the foothills of the mountain range that runs through Mindoro's interior and includes 20 km2 of the Mt. Iglit Refuge east of the refuge headquarters. Elevation ranges from 300 to 1000 m. Most of the study area is comprised of several ridges, and it is bounded by ranges of steep ridges to the north, east, and south. Two rivers flow year round and several streams flow only in