A semi-lunar rhythm appeared to be in the chick weight-growth curve of the Short-tailed Shearwaters (Puffinus tenuirostris) and exactly found in feeding of the Sooty Shearwaters (Puffinus griseus) to their chicks before desertion • by parents. These rhythms may be caused by periodicity in the availability of the krill, especially Australian krill (Nyctiphanes australis), the main food for chicks of both shearwaters. Comparing the chick growths in Tasmania with their mortality occurrences in

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... n in over a four year study of the Short-tailed Shearwaters, the best growth year of 1980 corresponded to a low mortality year, while a poor growth year of 1984 was situated at the peak of a mass mortality period of 1983-1985 in Japan. In the worst growth year of 1986, the mass mortality did not occur along Japan but Australia and the island of Guam. Therefore, the growth of chicks at the breeding site in Tasmania and mortality occurrences in Japan, Australia and Guam have a mutual relation, and they could be governed by the annual fluctuations in abundance of krill in Australian regions.