Ultrasounds are high-pitched sounds more than 20 kilohertz (kHz) in frequency, exceeding the upper limit of sounds detectable by humans, and far higher than the 12 kHz frequencies that most amphibians, reptiles and birds are capable of hearing and producing. Key parts of the ear must be specially adapted to detect ultrasounds -- namely, the eardrum must be very thin to vibrate effectively at these high frequencies, and the bones of the middle ear must be extremely lightweight in order to transmit ultrasonic vibrations to the inner ear. The presence of an ear canal not only protects A. tormotus' thin and fragile eardrum from the environment, but also lessens the distance between the eardrum and the inner ear, thus allowing the bones of the middle ear to be shorter, and as a result, lighter in weight.
Scientists have known for several years that A. tormotus males produce high-pitched, birdlike calls that extend into the ultrasonic range. What remained to be tested was whether the ultrasounds were a byproduct of the frog's sound-production system or were heard and responded to by other males of that species. Researchers Albert S. Feng, an auditory neuroscientist at the University of Illinois, Urbana-Champaign; Narins, who studies auditory behavior, neurophysiology and mechanics; and colleagues conducted behavioral and physiological studies to investigate A. tormotus' hearing ability.
The researchers first wanted to know whether A. tormotus can hear ultrasounds. They recorded a male's call, split it into the audible components and ultrasonic components, and observed the responses of eight A. tormotus males to each of the split sounds. Five of the eight frogs produced calls in response to the audible, ultrasonic or both components of the species call, and three did not. Results of the behavioral observations showed that males were capab
Source:University of California - Los Angeles