DELAY IN DEVELOPMENT OF AUDITION AND CHAN GE OF LEADING AFFERENTATIONDURING EARLY BEHAVIORAL ONTOGENY IN BIRDS

Development of auditory sensitivity was studied by recording microphon ic component of cochlear potentials during the period of opening the e yes in 6 species of birds with different types of ontogeny (Anas plath yrynchos, Larus canus and L. argentatus, Sterna paradisaea, Coloeus mo nedula and Corvus frugeleus). The onset of opening the eyes is accompa nied by a delay in development of auditory sensitivity and temporary d ecrease of upper frequency limit of the audible range. Before such a d elay acoustic afferentation is leading in feeding behaviour or in resp onse of following in nestlings or chicks. After the period of delay pu re tones lose the efficacy in eliciting feeding and following reaction s, and the correlation between the low-frequency range of increased se nsitivity and the efficacy of pure tone signals disappears, while the new peak of sensitivity appears which fits the maximal energetic compo nent of the parental acoustic signals. It seems possible that the dela y may be the result of brain temperature decrease while eyes open the thermoregulation being ustable. Such a delay may facilitate also the s ubstitution of acoustic afferentation for visual in the main behaviour al responses in early ontogeny.