Evidence for auditory localization ability in the turtle

Evidence is presented that the semiaquatic turtle Chrysemys scripta and the terrestrial turtle Terrapene carolina major can detect the direction of a tone within their sensitive area of hearing. It is further suggested that not only can these species respond behaviorally to sound without extensive manipulation but can use limited hearing in a problem-solving situation of maze learning. Adult emydid turtles (5 C. scripta, 3 T. carolina) learned a Y-maze with a 500-c/s signal to an invisible open goal box to avoid bright light. All animals performed above chance levels, but it required over 240 trials on the average to reach 60%-correct performance. Computations suggest that binaural cues used by mammals would not be adequately encoded by the primitive auditory systems of the species studied. It is further suggested that these turtles use bone conduction by coupling their ears to the substrate to hear vibrations in the immediate area. This would appear to be a carryover from the ancient reptile stem stock. The poor middle-ear impedance system relegates air-borne sound processing to be a somewhat insensitive limited low-pass system, depending heavily on monaural cues derived from head scanning. vocal output in these species appears to be spectrally imbalanced with their auditory sensitivity. The role of species-specific vocal signalling is unclear from the present data.