Some aspects of embryonic behaviour in the duck ( Anas platyrhynchos)

Abstract

A total of 321 duck (Peking and Mallard) and chick (White Leghorn) embryos were used in a series of observations and experiments on embryonic behaviour. In Part 1 it was demonstrated that the amount of motility (movements) which the duck embryo exhibits is specific to its stage of development. Movements begin on the 5th day of incubation at a rather low level and gradually increase to a peak between 14 and 17 days of incubation. After that time they decrease. This finding was the same regardless of which of three different methods was used to evaluate the motility. During the first few days of motility the movements are non-random and stereotyped. After day 9 they become relatively uncoordinated and jerky and are qualitatively different from the earlier movements. During much of the 27-day incubation period the embryo exhibits stage-characteristic periods of bursts of activity interspersed by inactivity. Beginning on day 22 (Part 2) the embryo begins a series of complex coordinated movements which serve to bring it into a characteristic hatching position. Between days 22 and 27 the duck embryo tucks its head under the right wing, penetrates its bill into the air-space, pips or cracks the shell and eventually hatches. The movements used for these various acts are described; their sequence and character is remarkably similar to the chick embryo. It was also demonstrated that both passive gravitational factors and active behavioural movements are responsible for the appearance of the first crack (pipping) in the upper part of the blunt or large end of the shell. Three different categories of head movements are recorded in Part 3; Back, Lateral and Other. Since back-thrust movements are an important part of hatching (climax) it was of interest to determine how they developed. It was shown that Back movements do not gradually increase in frequency between 21 and 27 days of incubation but rather they show a relatively sudden increase about 16 hr prior to hatching and another increase during actual hatching (climax). The earlier preference for right head turns which results in tucking was shown to disappear on about days 23 or 24 of incubation. In Part 4, both head movements and bill- or beak-clapping in duck and chick embryos were recorded before and after the right wing had been lifted from its normal position over the embryo's head. Contrary to earlier reports in the literature neither head movements nor bill- or beak-clapping was affected by this manipulation. The frequency of these various movements did not appreciably change.