Acoustic communication between bird embryos - clicking sound and hatch synchronization.

Besides vocalization, controlled by the syrinx, clicking sounds, clicks or clicking noise is another kind of acoustic communication between the embryos. They are developed in the last days before hatching, obviously with the onset of respiration, and are audible to the human ear. Embryonic clicking sounds have been demonstrated in turtles and various bird species. Hatching synchronization is widespread in the animal kingdom from insects to birds. The role of clicking sounds in hatching synchronization has only been studied in a few species, e.g. in poultry such as ducks, quails and chickens. This review paper aims to show an overview of the state of the art, including former own research on clicking sound production and hatching synchronization in ducks, and would like to encourage more attention to be paid to this phenomenon in artificial incubation. Literature search was done using Google Scholar and the electronic data basis of PubMed, Science Direct and Europe PMC. Former own experiments were carried out with Muscovy duck hatching eggs during the last week of incubation, incubated at 37.7 ± 0.3°C and 50-60% rel. air humidity. Clicking sound was recorded non-invasively by microphone at the eggshell. The development of clicking sound with increasing embryonic age until hatch and the relationship of clicking sounds and hatch synchronization under different sound pressure levels (steps of 5 dB) were investigated. The literature search revealed that, apart from the classic works, there are only a few systematic studies on this topic. The proportion is even smaller when it comes to studies between clicking sound and hatch synchronization and possible mechanisms. Former own systematic investigations in Muscovy ducks have shown, that: - clicking sounds were produced synchronously with respiration movement - hatch synchronization by clicking sound depends on ambient noise level; at a noise level of more than 80 dB clicking sound communication was disturbed. Conclusions: Hatching synchronization by clicking sounds could also be important for commercial poultry incubation. Further systematic studies on the ontogeny and the association of clicking sounds with hatching synchronization in different poultry species and lines, as well as on the role of technical background noise in incubators, are needed. [ABSTRACT FROM AUTHOR]