[A delay in the development of hearing and a shift in the leading afferentation in the early behavioral ontogeny of birds].

Development of auditory sensitivity was studied by recording microphonic component of cochlear potentials during the period of opening the eyes in 6 species of birds with different types of ontogeny (Anas plathyrynchos, Larus canus and L. argentatus, Sterna paradisaea, Coloeus monedula and Corvus frugeleus). The onset of opening the eyes is accompanied by a delay in development of auditory sensitivity and temporary decrease of upper frequency limit of the audible range. Before such a delay acoustic afferentation is leading in feeding behaviour or in response of following in nestlings or chicks. After the period of delay pure tones lose the efficacy in eliciting feeding and following reactions, and the correlation between the low-frequency range of increased sensitivity and the efficacy of pure tone signals disappears, while the new peak of sensitivity appears which fits the maximal energetic component of the parental acoustic signals. It seems possible that the delay may be the result of brain temperature decrease while eyes open the thermoregulation being unstable. Such a delay may facilitate also the substitution of acoustic afferentation for visual in the main behavioural responses in early ontogeny.