山階鳥類研究所研究報告
Online ISSN : 1883-3659
Print ISSN : 0044-0183
トキにおける羽色変化の機構
内田 康夫
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ジャーナル フリー

6 巻 (1970-1972) 1-2 号 p. 54-72

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Although white and grey forms had long been known in Japanese Crested Ibis Nipponia nippon, its scarcity prevented detailed research. Contrary to a former opinion that these were color phases, Mr. H. Sato (1957) considered them as seasonal forms and later suggested (1968) that the grey form is caused by cosmetic coloration toward breeding season.
This paper presents a detailed analysis on the mechanism of this type of color change based on numerous feather samples offered to Yamashina Institute by Mr. Y. Muramoto who collected them in its natural habitat in Ishikawa for many years. Supplemental observations were made with live birds in Sado I. with valuable assistance of Messrs. K. Chikatsuji and T. Takano of Ibis protection Center. Histological studies were made by the author at Department of Zoology, Tokyo University.
Some important points clarified in this paper are as follows:
1. The feather samples suggested neither of the known types of color change: 1) molting, 2) abrasion, 3) cosmetic staining with color substance in preen oil, 4) photo chemical change of biochrome in the feather, and 5) external staining (e. g. iron in water birds).
2. Under the feathers surrounding the naked face of Japanese Crested Ibis, a particular area of the skin was found producing 'black substance.' (Fig. 12).
3. A few tiny samples of this black substance fell on the snow when a captive ibis scratched that region of the head (Fig. 13, 14). These could be collected and used for chemical analysis (to be published elsewhere).
4. Prior to the breeding season, in late January through February, a characteristic behavior of rubbing the side of its head to the shoulder region was observed after bathing. This was named 'daubing behavior' (Fig. 16) and it lasted 20-30 minutes followed by normal preening.
5. The grey, or rather blackish, tint of the neck to shoulder region got deeper as the 'daubing behavior' was repeated.
6. Histologically, it was proved that the grey tint was caused by external adherance of 'black substance' to the proximal (not distal) barbules of the normal white feathers (Fig. 4-10).
7. The black substance on the feathers and those picked up after head scsatching were identical microscopically and chemically. These are supposed to come out along feather pores of the skin, since the feathers of the black substance producing area had black ring near the root of the rachis (Fig. 2, 9, 10).
8. The change from grey to white form occurred by normal post-nuptial molting (Fig. 17) and neither 'daubing behavior' nor dropping of black substance was observed after bathing in this period.
9. The 'daubing behavior' was so important in this new type of plumage color change that even during the critical period of change from white to grey form, the white plumage remained untinted unless this behavior was performed, which always occurred after bathing. Five to six bathing-'daubing behavior' sequences completed a typical grey form. The first bathing of the season was observed on a fine day in late January.
10. Physio-ethological mechanisms and the hormonal control involved were analysed (Fig. 20) and significance of the grey form was discussed eco-evolutionarily.

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