PERIHATCHING BEHAVIOUR PATTERNS OF CHICK EMBRYOS (GALLUS-DOMESTICUS)

Perihatching behaviour is analysed in terms of changes in the frequency of performance of three behaviours; vocalization, eyelid raising and head raising. Three distinct phases of development are described. Though 79 per cent of the animals displaying phase 1 behaviour do enter phases 2 and 3 of development, we could not predict from phase 1 performance patterns the time at which phase 2 would occur. The manipulations of chorio-allantoic membrane puncture at 432 and 451 hr of incubation, and removal of the chorio-allantoic and amniotic fluids at 451 hr of incubation afforded a greater predictability of hatching times than did the control groups. None of the above experimental groups however differed from one another in their distributions of hatching times. As a result of these experiments we postulate that at a given stage of development, chicks become responsive to some change in function in the chorio-allantoic membrane. A process then is instituted within the animal that continues for a minimum time before hatching can occur. We then suggest possible sources of the chorio-allantoic stimulus to which the animals respond, and sources of the response processes themselves that finally lead to hatching. Finally we suggest experimental approaches that can lead to the identification of these stimuli and response processes. © 1969.