In central India, most Gaur mate in December and January, and calves are born in August and September according to Dunbar Brander (1923); Stebbing (1911) and Sanderson (1912) generally agreed with Dunbar Brander but noted that calves may also be born in April, May, and June. In Kanha National Park (central India) Schaller (1967) recorded rutting bulls from December to June, with an apparent peak of sexual behaviour in March and April; however, the occurrence of a few new-born animals throughout the year indicated that some mating must occur in every month. In southern India the majority of matings reportedly take place between November and March (Morris 1937). In Cambodia the majority of Gaur births occur in December and January (Wharton 1957). In Myanmar, calves are born throughout the year (Evans 1912; Peacock 1933); and in West Malaysia young Gaur are seen in all months except October to December (Hubback 1937).
The gestation period of Gaur is reported to be nine months by Hubback (1937) and Crandall (1964) and 270 days, ‘a little shorter than for Banteng or domestic cattle and longer than for yak and Kouprey’, by National Research Council (1983: 49). Only one calf is born to a cow per pregnancy; there are no records of twins (Hubback 1937; Schaller 1967). Females probably first mate when about two years old and thus have their first calf at three years old (Schaller 1967). If the food supply is favourable, most adult females probably calve every year. In Kanha National Park, approximately 90% of adult cows bore young during a year but calf mortality was high, with about 50% of the calves dying before reaching one year old; the main cause of death was predation by Tigers Panthera tigris (Schaller 1967).
Rarely, bulls kill each other when fighting, and occasionally they are severely injured while fighting. Predation is by far the major cause of Gaur mortality, perhaps followed by disease (N.S. Kumar pers. comm. 2008). For example in Bandipur, Gaur is the most important prey in terms of the biomass taken by Tiger (42%) and Leopard Panthera pardus (15%) (Andheria et al. 2007). In Bandipur, Gaur remains were found in about 24% of Tiger faeces and 9% of Leopard faeces (Andheria et al. 2007). In adjoining Nagarahole, the proportion of Gaur in Tiger’s diet was about 45% in kills, 17% in scats (Karanth and Sunquist 1995). In Tadoba-Andhari, Gaur together with Sambar contributed to nearly 70% of the prey biomass consumed by Tiger, whereas in Pench-Maharashtra it was 80% (Karanth and Kumar 2005). In well protected forest RESERVES where different body-sized ungulates are abundantly available, Gaur is selectively predated by Tiger (N.S. Kumar pers. comm. 2008).