 Males are sexually mature by the time they are a year old , though successful mating generally occurs only after four years . Mature males start establishing territories and try to gain access to females . Females can conceive after they are a year and a half old ; oestrous lasts for 24 to 48 hours , and occurs every 12 – 29 days in non @-@ pregnant females . The annual three @-@ week @-@ long rut ( breeding season ) begins toward the end of the wet season , typically in May . <unk> growth and hormone production in males begin a few months before the breeding season , resulting in greater aggressiveness and territoriality . The <unk> glands are heavier , testosterone levels are nearly twice as high in territorial males as in bachelors , and the neck of a territorial male tends to be thicker than that of a bachelor during the rut . Mating tends to take place between full moons . 
