Growth and Development of the Black-eared Kite Milvus migrans lineatus
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概要
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The growth and development of known-age, nine Black-eared Kite nestlings from four nests were investigated in the vicinity of the Wakimisaki fishing-port, situated at the southern edge of the Nagasaki peninsula, Nagasaki Prefecture, in 1984. The results obtained are summarized as follows.1) The second down appeared on the body by 9-12 days after hatching, and the body feathers emerged at 18-22 days. The nestlings began standing on both legs at 17-19 days and flapping their wings at 27-31 days. They began to eat prey animals by themselves at 45-47 days.2) Some diurnal raptors rear a young each brood (Bl species) and some others raise two or more young (B2 species). Of the four nests examined, three nests each contained two nestlings, and a nest had three. Therefore, the Black-eared kite belongs to the B2 species. At one nest the younger and elder nestlings increased their body weight at the same growth rate; at two nests the younger sibling(s) gained slower their body weight than did the elder. At the other nest, the younger chick died of starvation. Judging from the uniformity of the environmental condition in relation to food availability among the four nests, it seemed that the foraging ability of the parent kites varied with the individual and influenced the survival and growth of younger sibling(s).3) The growth rate constant of the logistic equation fitted to weight data for each nestling averaged 0.133. This value did not differ significantly from the expected value of 0.169, which was calculated by the equation correlating the growth rate constant with the asymptotic body weight for 27 species of the B2 diurnal raptors.4) The emergence of body feathers and the initiation of standing on both legs tended to occur at an earlier growth stage in large raptors than in small ones. In this connection, it was concluded that the Black-eared Kite, in spite of being a medium-sized raptor, possesses about the same developmental pattern as that of the large raptors rather than that of small or other medium-sized ones.
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