A big bamboo bush surrounding the duck-netting pond at Koshigaya, Saitama Pref., situated at southern central part of Kanto Plain, is used as winter roost by 30, 000-50, 000
Sturnus cineraceus (with annual difference in 1960, 1967, 1968). Its winter status has already been reported (Misc. Rep. Yam. Inst. No. 18, 1962), and here, the monthly fluctuation of the roosting flock in 1967-68 is described. Flocks returning to the roost were counted at a fixed observation point before the roost and were tallied later by 10 minutes intervals, and by directions.
1. The size of roosting flock fluctuated as follows: Oct. 16, 1967: 14, 840 birds, Nov. 23: 19, 510 birds, Dec. 13: 22, 553 birds, Jan. 10, 1968: 29, 398 birds (Feb. 2, 1960: 49, 700 birds), Feb. 14: 24, 150 birds, Mar. 3: 17, 016 birds, Mar. 17: 6, 995 birds, Apr. 6: 850 birds, May 6: 172 birds, June 5: 30 birds, July 10: 1, 183 birds, gathered, but not roosted, and flew to NE (to the summer roost at Omatsu), Aug. 5: Some 140 birds and other overflying flocks flew to NE., Oct. 21: In this year still only 500 birds roosted in this month (owing perhaps to new house construction before the roost), Nov. 11: 41, 959 birds roosted, but 2, 260 birds flew to NE (to summer roost), and other 2, 070 birds to another direction (to NW). The roost in this direction was not confirmed, but this may be a small subsidiary roost used when the main roost became too crowded.
2. Thus, the Koshigaya roost was confirmed to be a winter roost and summer roosts were found, as the result of roosting flight observations at various places of feeding area.
3. There were two summer roost sites, the one at Hirakata village 5km northward and the other at Omatsu 4km northeast.
4. The Hirakata roost consisted of three different bamboo bushes surrounded by trees or small cryptomeria wood (here some Little egrets and Night herons roosted). However, the bamboos were dying (it was dying over extensive area in Kanto plain in this year) and flocks that gathered were observed to move to Omatsu roost, 3km apart, but about 2, 500 birds remained to roost.
5. The Omatsu roost was a big one, formed in the bamboo bush of a temple where about 20, 000 birds gathered from all directions, including Koshigaya area. Thus, Koshigaya roost had in summer no more value than a mere feeding site or a gathering point on the roosting flyway to Omatsu.
6. The populational roost change by summer and winter may depend principally on the change of status of the feeding areas. The Koshigaya area is extensive rice fields which serve as the best winter feeding ground but after the rice has grown in early summer, the area no more fits as feeding ground and although some vegetable fields are mixed, they are dry. In the nerthern area, the vegetable fields are prevailing and are cultivated in well watered conditions. More over, villages are scattered with well wooded surroundings where much tree fruits are available as summer food. Thus, the population moves to this area and censequently the roost is sought in that area. It may seem that the roost has its significance only when the surroundings are fit for feeding grounds.
7. All the roosts were so situated as one side facing to a river with not easily accessible edge of the roost.
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