Molt of Barn Swallows in Japan

Abstract

Molt data for Barn Swallow (Hirundo rustica) were collected during banding research conducted in five areas of Japan; Okinawa, Kagoshima, Fukuoka, Aichi and Tokyo. Swallows were banded from late August to early September in Kagoshima, from mid to late September in Okinawa, in early August in Tokyo and Aichi, and during mid July in Fukuoka. All captured swallows were banded with metal rings, and molt status was recorded for most of the birds. Analysis of the data shows that molting commenced in mid July. By early August 61% of banded birds were in molt. The percentage of molting individuals was 88% from late August to early September; and 83% from mid to late September. Over 99% of the banded juvenile birds were not in molt. Some of these second year birds may not have completely molted into adult plumage.
Some suspended molt was observed, at a ratio of 0% in mid July and 7.1% in early August for Tokyo, 44.6% from late August to early September in Kagoshima, and 70.4% from mid to late September in Okinawa. The ratios of suspended molt observed in this research are higher than those reported for Europe. This may be due to differences in migration routes. In Europe most of the migration occurs over land, with only a short 15 km stretch of ocean across the Straits of Gibraltar. In Asia, however, banding research indicates that swallows migrate from breeding grounds in Japan along the Ryukyu Islands to wintering areas in island and mainland Southeast Asia. The suspended molt observed in Japan may help the swallows avoid a loss in flight efficiency required for the long migration over open water.