[Role of natural sensory factors in organization of feeding behavior using fledgling development as an example].

A change in the composition of natural sensory stimuli, triggers of the alimentary functional system of Muscicapa hypoleuca nestlings, was studied throughout their nest life. In the first five days the alimentary reaction is elicited by a complex of acoustic stimuli. From the fifth to the eighth day the reaction appears in response to a momentary change of illumination. From the ninth to the thirteenth day two stimuli are involved in the organization of the alimentary reaction: a trigger stimulus-a momentary change of illumination, and a directional stimulus-a mobile silhouette of the bird. On the thirteenth to the fifteenth day the alimentary reaction appears only in response to the bird's movement. It is assumed that the successive change of trigger stimuli in one and the same alimentary functional system is determined by a successive involvement of increasingly complicated sensory mechanisms. The time periods of involvement may vary with a change of environmental factors.