Prenatal Behavior of Birds

An analysis of behavioral, neurological, and biochemical research indicates that the sensory systems of the avian embryo become functional in the following order: (1) non-visual photic sensitivity; (2) tactile sensitivity; (3) vestibular sensitivity; (4) proprioception; (5) audition; (6) vision. There is no firm information about the onset of gustation and olfaction in the avian embryo. With the possible exception of vision, there would appear to be adequate stimulation during the normal course of incubation to excite all the sensory systems. Whether such stimulation actually plays a role in regulating species-typical sensory and perceptual development is not known. While it seems doubtful that depriving the embryo of relevant stimulation, or prematurely exposing it to such stimulation, would alter the absolute sequence in which the sensory systems develop, such a manipulation might exert some effect on the relative time of onset of the particular sensory system involved, and a major effect on the development of adaptive perceptual discrimination abilities within the modality thus affected. An experiment involving sub-total auditory deprivation demonstrated in duck embryos that normally occurring auditory stimulation is essential to the development of species-specific auditory perception. Although partially deprived embryos were not capable of making the usual perceptual discriminative response, they were capable of hearing. Similarly deprived embryos were able to make the species-specific auditory discrimination after hatching, indicating that the sub-total deprivation induces a lag in the development of an embryo's discriminative ability. These findings are consonant with the view that exposure to relevant stimulation plays an important role in regulating the development of adaptive perceptual discrimination abilities in the avian embryo.