Males of the Australian whistling moth Hecatesia exultans produce ultrasonic acoustical signals while perched on low vegetation. Some males call more or less continuously for several hours during midday with individuals occupying the same general calling area for up to several weeks. The nearest neighbour of calling males is typically 15 to 25m distant, at the outer edge of the estimated range at which neighbours can detect each other's ultrasonic signals. Calling male intruders occasionally enter an occupied territory, resulting in aerial clashes with nearly continuous signalling by both combatants. Males respond to playback of taped signals by flying toward the speaker and sometimes by calling while perched on or near the speaker. Females sometimes visit calling males, with copulation following very soon after the female alights on vegetation near the male's perch. Males increase the rate of sound production by about 11% when presented with moving pinned specimens or paper models of conspecifics. These observations and experiments indicate that males use ultrasound as long-distance communication signals designed to attract sexually receptive females and to establish territorial residency in competition with other males.