[Acoustically guided behavior in the early ontogeny of the long-eared owl: the development of hearing sensitivity].

The development of hearing sensitivity was studied in 15 nestlings and 7 adult long eared owls by cochlear recording potentials. The dynamic of frequency threshold characteristics of cochlear microphonic, action potential of cochlear nerve, and electromyogram of reflectory contraction of middle ear muscle were followed from the 1st to 40 day posthatching. The upper limit of hearing determined by cochlear microphonic, was about 3 kHz on the 1st day after hatching, 7 kHz on the 6th day, and 10 kHz on the 11th. Within 11 days after hatching the low-frequency range of higher sensitivity was revealed (with the maximum at 0.5 kHz), which was the same as that of monotonic signals effective for stimulation of the feeding reaction. The middle frequency range of higher sensitivity corresponded to the spectrum of own vocalization of the nestlings. During the period of formation of the patterned vision there was a delay in development of low- and middle-frequency sensitivity of cochlear microphonic while the high-frequency thresholds continued to decrease. After this period the guiding stimulation for eliciting feeding reaction changes from the auditory for the visual. The action potential of the cochlear nerve could be recorded from the 6th day simultaneously with the appearance of locating head movements and the reflectory contraction of the middle ear muscle.