北海道東部に生息するタンチョウの2001年春の繁殖状況

概要

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Three aerial surveys to monitor the breeding status of the Tancho or the Red-crowned Crane Grusjaponensis were carried out in eastern Hokkaido, Japan, from late April to mid June of 2001. We found 263 breeding pairs in total, the largest number so far: 30(11.4%) in Tokachi, 134(50.9%) in Kushiro, 98 (37.3 %) in Nemuro and 1(0.4%) in Abashiri district. Their distribution areas were very slowly expanding and the number of pairs mainly increased in Nemuro, especially in Lake Furen and Notsuke Peninsula areas this year. Average distance of the nearest nests was 2,191m and density of breeding pairs in wetlands became slightly higher than that of the previous year: 1.33 per km^3 in Tokachi, 0.41 in Kushiro, 1.29 in Nemuro, and 0.03 in Abashiri, respectively. At the first survey 67.2% of the population were engaging to breed and 89.7% of all breeding pairs already nested during late April-early May. Most of the nests were laid on the open wetlands, but we observed 16 (5.9 %) nests in some dense alder woods. It was suggested that 6.8 % of pairs re-nested at different spots from their first ones and a pair repeated thrice to construct nests with egg-laying during April to mid June. There were 69 brooding pairs with 96 chicks and average number of chicks per family was 1.39 in late May, 0.2 higher than that of the previous year.
2001-12-30