Banding research has been conducted continuously along the Sekiya Coast of Niigata City since 1987. Over this period, more than 14,000 Bush Warblers of Japanese origin have been banded and released. Almost all of these have been
Cetta diphone cantans, but a small number of
C. d. sakhalinensis may also be included. The results of this research have helped clarify variations in the timing and size, as well as the destinations, of the Japanese Bush Warbler seasonal migration. Among the banded Bush Warblers, however, have been two specimens of continental origin,
C. d. borealis. These two specimens were distinguished based on external characteristics, and basic measurements and photos are included in this report.
The banding research is conducted inside a protected area surrounded by a steel fence, within a coastal park. Vegetation in the area is a typical coastal forest dominated by pine (
Pinus thunbergii), but with various species of deciduous and evergreen broad-leaved trees mixed in. The undergrowth consists of shrubs, and there is also a manmade pond surrounded by lowgrowing bamboo grass, where the banding research is conducted using ten to twelve mist nets (ATX and HTX).
One of the individuals identified as
C. d. borealis was an adult female captured on 17 Oct., 1999. Visual inspection was sufficient for distinguishing this continental bird from Japanese individuals captured at the same time (Fig 1-Photo A and B; Table 1-No.1). The continental form shows a much heavier brownish tint, especially on the crown, back, breast, and tail, as compared to the more olive coloring of the Japanese subspecies. The second individual was an adult male captured on 25 April 2008 (Fig 1-Photo C, D and E; Table 1-No.2), and was noticeably larger than
cantans.
Previously only two captures of
C. d. borealis had been obtained from Japan; one male in May of 1993 on Rebun Island off the northern coast of Hokkaido; and one female in August of 2005 at Yonago City in Tottori Prefecture, west of Niigata. Visual confirmations as well only amount to several incidents. It is thus believed that these records all represent accidental birds that had strayed off their regular migration route, which runs from Taiwan and central China to the Korean Peninsula.
Banding records from Niigata and elsewhere indicate that subspecies
cantans migrates along the Sea of Japan coastline, with peaks in April and September. As the timing of the subspecies
borealis migration overlaps with that of
cantans, it can be expected that further records of the continental species may be obtained in future banding research.
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