CHEMOSENSORY LEARNING IN THE CHICKEN-EMBRYO

Prenatal chemosensory learning has been demonstrated in mammals, fish, amphibians, and insects, but not birds, although there is evidence of the avian's ability to learn auditory stimuli before hatching. This p aper examines how exposure to a chemosensory stimulus (strawberry) pri or to hatching affects subsequent chemosensory preferences of newly ha tched chicks. The chicks' preferences were assessed at 2 days after ha tching using an ''olfactory'' preference test (strawberry-smelling sha vings versus water-coated shavings) and at 4 days after hatching using a ''gustatory'' preference test (strawberry-flavoured water versus un flavoured water). Chicken embryos were exposed to strawberry from Day 15 to Day 20 of incubation by either presenting the odour in the air a round the egg, rubbing it onto the shell, or injecting it into the air space. With no exposure to strawberry before hatching, strawberry was highly aversive to chicks after hatching. However, following exposure to strawberry before hatching, chicks expressed a greater preference for (or weaker aversion to) the strawberry stimulus. Chicks exposed to strawberry before hatching drank more strawberry flavoured water and spent more time in a strawberry-scented area than chicks having no exp osure before hatching. This change in preference was specific to the s timulus experienced before hatching and was present in the absence of any posthatching exposure to the stimulus. The results demonstrate tha t a chick's chemosensory preferences are changed as a result of experi ence with a stimulus before hatching and are suggestive of learning. T he results, similar to those obtained in other animal groups, indicate the universality of ''prenatal'' chemosensory learning in the animal kingdom. A possible role of embryonic chemosensory learning for recogn ition is discussed. (C) 1998 Elsevier Science Inc.