Horsfield's tarsier is monogamous, with a copulation frequency during estrus of once per night. Courtship calls are performed by the male and he emits 2-3 chirrups while opening and closing the mouth. This call happens within 5 minutes of looking at the female. Once the male gives his courtship call, if the female is receptive, she will perform genital displays to him. If the female is not in estrus, she will emit an agonistic call which is often followed by biting and pushing the male away. Both sexes' calls last on average for 1 second, and the interval between calls is on average 3 seconds.