Hearing, single-unit analysis, and vocalizations in songbirds.

Auditory neurons in the avian cochlear nucleus are systematically arranged according to their best frequencies. The thresholds of single auditory neurons at their best frequencies match the thresholds of hearing obtained by behavioral methods for the same frequencies. The upper range of single-unit best frequencies shows distinct interspecific variation which is correlated with the differences in the range of vocal frequencies. Most songbirds do not seem to produce frequencies below I kilohertz but can hear them.