Abstract:In this review the development of acoustic communication between embryos or between embryos and chicks as well as between embryos/chicks and the breeding parents will be addressed. Special emphasis is given to the impact of embryonic acoustic signals for hatching synchronization.In the Muscovy duck (Cairina moschata L. f. domestica) clicking sound communication is absolutely essential for a synchronized hatching. The mechanism underlying this special case of communication is a synchronization of clicking rates. In a clutch, embryos adapt their clicking rates to each other. Clicking rates of less developed embryos rose faster (acceleration) than clicking rates of more developed embryos (retardation). No evidence was found that vocalization of embryos, chicks and parents improve hatching synchronization.Although, many authors assume that prenatal acoustic interaction by vocalization (an exchange of acoustic signals) exists, in the Muscovy duck it was shown that an acoustic interaction started when the first embryo had hatched. Specific call types serve as communication-releasing signals. Acoustic mother-duckling interaction developed later and gradually during the process of nest-leaving also based on specific call types.Measurements on sound transmission indicate that all embryos within a clutch are in mutual acoustic contact.
Between spring 2001 and autumn 2004, the habitat use, vertical migration, and density of Mysis relicta in the lakes "Breiter Luzin" and "Schmaler Luzin" in northeastern Germany were investigated by horizontal net hauls, epibenthic sledge hauls, and SCUBA diving. On 3-4 July 2001 we estimated a density of 466.03 ind./m 2 in the water column of lake "Breiter Luzin", but in April of 2002 population density was only 5.26 ind./m 2 . In October 2004 the observed densities increased with depth, starting at the lower sublittoral down to the upper profundal on about 1000 ind./m 2 . Downward from 22 m, densities fluctuated around this value up to 30 m depth. During daytime, mysids were never observed above 9 m. Below this limit all suitable parts of both lakes were occupied. We found no evidence for a preference of different sediment types as mud or sand. During daytime mysids showed a strong affinity for the lake bottom, and adults tend to live in deeper areas than juveniles. At night this distribution seems to be inverted. In July 2001 the proportion of adults (especially females) was highest in the metalimnion and the upper hypolimnion, whereas the proportion of juveniles increased with depth.
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