Sound Production by a Coral Reef Fish (Pomacentrus partitus): Evidence for a Vocal, Territorial "Keep-Out" Signal

The Chirp-sound, produced by males of the bicolor damselfish Pomacentrus partitus, plays an important role in influencing the behavior of conspecific females during the pre-spawning period. Evidence is provided here that the same sound possesses another function, i.e., it is a vocal, territorial "keep-out" signal. A field-study, conducted on a reef off southern Florida, showed that such sounds, when transmitted by an underwater loudspeaker from unguarded territories (residents removed), can inhibit territorial intrusion by neighboring male conspecifics for a significantly longer time than when such sounds are not transmitted from a territory. Evidence was also obtained that the visual presence of the resident was a more effective deterrent to intrusion, however, than sound-transmission. Finally, a significant relationship was found between the size of a given territory and the time of territory-intrusion by a neighboring conspecific male, suggesting that neighbors are aware of the resource-holding potential of territorial residents. A brief laboratory study also indicated that the Chirp-sounds of a resident were a more effective deterrent to territorial intrusion than Chirp-sounds of non-residents. Transmission of other sounds from unguarded territories, including random noise and feeding stridulations by residents and non-residents, showed no deterrent effect on territorial intrusion.