Abstract
It is possible that breeding populations of local birds are affected when the birds' breeding environment and food resources are contaminated by radioactive substances. Since birds have considerable capacity for movement and dispersal, not only population data but also the birth rate (productivity) and the survival rate are important parameters when investigating breeding populations. Since the late 1980s, Europe (CES, Constant Effort Site Ringing) and the USA (MAPS, Monitoring Avian Productivity and Survivorship) have been conducting standardized monitoring of bird reproduction using individual marking at a national scale. These investigations provide data (such as population index, birth rate index and adult bird survival rate index), which enable us not only to understand the dynamics of bird populations, but also to understand the variables affecting those dynamics. General census methods counting individual birds cannot obtain survival rate data, making it difficult to analyze factors affecting population change. In Japan, we started monitoring during the breeding season, as mentioned above. Monitoring was conducted at sites in Hokkaido (2) and in six prefectures, including Fukushima (3), Niigata (1) and Tottori (1). By comparing indexes for population, birth rate and survival rate for each year, we can detect yearly changes (from fixed-point observation) and place-dependent differences, even on a global scale. These data are expected to become a powerful tool for evaluation of short- and long-term influences on birds from the radiological pollution from the Fukushima Nuclear Power Plant accident. Common reed Bunting (Emberiza shoeniclus) is widely distributed over the Eurasian Continent. In Japan, it breeds in Hokkaido and in the northern part of Honshu, and it winters in the southern part of Honshu, Shikoku and Kyushu. 15 000–20 000 are ringed annually in Japan, and the total number ringed since 1961 is approximately 440,000. This is the second largest number ringed following 900,000 of Black-faced Bunting (Emberiza spodocephala). Common Reed Buntings breed in wetlands and grassland, and mainly inhabit reed beds during the migration and wintering period. Abnormalities in the tail feathers of Common Reed Bunting were found at the Fukushima-lagoon monitoring station at Niigata Prefecture in October 2011. Since, the phenomenon had never been observed before at that place, we called bird-banders from all over Japan to collect data of tail anomalies. Data from 17 places in 14 prefectures from Fukushima to Kagoshima were reported up until Spring 2012. Abnormalities of the tail feather were found in 767 out of 5541 birds. The abnormalities were found at all of the localities examined, but the frequency varied from place to place. Of the locations where >100 birds were released, Iwata city in Shizuoka had the highest frequency (25.6%), the second highest frequency was recorded at Yasugi city, Tottori (20.1%), and the lowest frequency was found in Oota-ku, Tokyo (1.6%). Almost all abnormalities were found in juveniles (97.3%). It was reported that abnormality in length in the tail feathers or partial whitening were observed of Barn Swallows in Chernobyl. Although that was said to be associated with radiaoactive materials, that observation is not consistent with our findings. Some parts of Common Reed Bunting population pass through Fukushima prefecture during migration, but it is unlikely that their genes will be altered during the short period of stay. Similar tail abnormalities were found all over Japan in the following years. Recently, tail abnormalities are also found on other species including Black-faced Buntings and Siberian Rubythroats (Luscinia calliope). Further investigation is needed on this matter, including the cause of this phenomenon.
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