To estimate the population size and distribution of migrant Brent Geese Branta bernicla in Japan, the Eastern Hokkaido Brent Goose Research Network organized simultaneous counts during autumn, winter and spring for 3 years between 2014 and 2017. Out of the 32 survey sites in Japan, 27 sites recorded one or more individuals. Among these sites, 16 sites recorded more than 65 individuals, which is a threshold number representing 1% of the estimated regional population (Ramsar Criterion 6). Those sites are considered to be important for migration, and include Kunashir Island, Notsuke Bay, Lake Furen, Hamanaka/Biwase, Akkeshi Bay, Urakawa, the vicinity of Date, the eastern part of Oshima Peninsula, the vicinity of Hakodate Bay, the vicinity of Shimokita Peninsula (Aomori Prefecture), the vicinity of Mutsu Bay (Aomori Pref.), the Pacific Ocean coast in Aomori Pref., Iwate Pref., Minamisanriku 1 (Miyagi Pref.), Minamisanriku 2 (Miyagi Pref.), and the coast of Gamou (Miyagi Pref.). The maximum total population recorded in these counts was 8,602, which was recorded in the autumn of 2015 and more than 84% of the total (7,233), was recorded in Notsuke Bay. The population size for Brent Geese that visit Japan was estimated to be approximately 8,600 in autumn, 2,500 in winter and 3,100 in spring. Eighty to ninety percent of Brent Geese in Japan during autumn and spring migrations concentrated in an area including Notsuke Bay and southern Kunashir Island, and the ratio of birds that visited southern Kunashir Island was higher in spring. When evaluating the number of birds observed overwintering in Japan (2,500), and the number of spring passage birds observed in eastern Hokkaido (3,100), the wintering sites and spring migration routes of up to 60% of the observed fall passage migrants (8,600) are unknown.
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