On the basis of 125 light-house struck specimens of the Gray's Grasshopper Warbler
Locustella fasciolata, distribution, migration routes and their origins were discussed. Specimens were sent from the following light-houses: Mizunoko (Oita Pref.), Sada-misaki (Ehime Pref.), Kyoga-saki (Kyoto-fu), Hegura-jima (Ishikawa Pref.), Nyudo-zaki (Akita Pref.), Omae-zaki (Shizuoka Pref.) and Shiriya-zaki (Aomori Pref.). Specimens and sight records from many other light-houses in Honshiu, Hokkaido, Southern Kuriles, South-west of Korea, northern Formosa since 1924 were also taken in consideration.
The breeding grounds of this species are from the upper basin of the Yenisei River to Amur district ranging from the south of 55°NL. and north of Hokkaido, and wintering grounds are Philippines, Celebes, Papuan islands etc.
Spring migrants pass through Honshiu during late May and middle June, and autumn migrants during late August and early October. Thus, spring migration period is shorter than in the autumn. The breeding season is relatively short in this species and most birds are already in breeding condition on spring migration. It seems, therefore, that they reach the destination taking the shortest route soon to breed on arrival. In the autumn, on the other hand, they have finished their breeding and include young birds. Thus, they also take inland routes other than the shortest coastal passage.
Four migration routes were suggested: 1) Philippines-East coast of Formosa-Riu Kiu-Honshiu-Japan Sea coast of Honshiu-Hokkaido-Kuriles and Sakhalin. 2) Philippines-East and west coasts of Formosa-Fuhsien-Chiensoo-South west of Korea-West coast of Honshiu and joins to 1. 3) Philippines-East and west coasts of Formosa-Fuhsien-Chiensoo-Korean Japan Sea coast and Usuri districts. 4) Philippines-Both coasts of Formosa- Fuhsien-Chiensoo-Shantung-North eastern China Upper basin of Yenisei River.
Five possible migration routes in Honshiu were also suggested as follows: A) Riu Kiu-Bungo Channel-Osaka Bay-Wakasa Bay-Japan Sea coast of Honshiu-Hokkaido. B) Bungo Channel-the Sea of Suo-Japan Sea coast and joins to route A. C) Deviated from route A at Osaka Bay-Ise Bay central Honshiu-Hokkaido. D) Deviated also from route C at Osaka Bay-the Pacific coast of Honshiu and joins to C. E) South west of Korea-west coast of Honshiu and joins to A. Among the five routes, A and E are presumably the heaviest and D is practically very seldom used, especially in spring migration.
The history of the present distribution and migration routes were also discussed. It was assumed that the earliest migration route taken in the geological age, was exclusively the route 1. However, other westward routes were later established with the change of coastal line caused by the submersion of land, and this westward swing of their migratory routes resulted the extention of their breeding range into Siberia.
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