山階鳥類研究所研究報告
Online ISSN : 1883-3659
Print ISSN : 0044-0183
ISSN-L : 0044-0183
ムクドリの調査第3報
蕃殖期から秋への就塒行動(1.東京以東)(附採餌行動)
黒田 長久
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ジャーナル フリー

1960 年 2 巻 14 号 p. 18-29

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Observations on the roosting behaviour and the change of roost during and after breeding are reported. In conclusion, the factors for selecting roost are as follows: 1) Safety and the environment, 2) Presence of both roosting and gathering places, 3) Kind of plants, 4) Size of roost, 5) Correlation with flock size. Although there existed many bamboo thickets, those selected for roosts were always adjacent to the rice paddies which made them less easily approached by man. The kind of roost was, beside bamboo thicket, reed beds of river side, desiduous trees as well as pine trees. These roosts were not necessarily selected seasonally, though in winter bamboo thickets were always used. It also seems that they determine the roost size by their flock size, thus in August, a flock of about 400 birds used the extensive bamboo thicket (as in winter) in 1955, but less than 100 birds roosted in the pine trees nearby, in July, 1956 and August, 1954.
The factors for change of roost may be as follows: 1) Environmental factors (a. Change of feeding grounds, b. Movement of the flock due to a), 2) Natural or human factors, 3) "Special attraction, " 4) Overpopulation ("flooding effect"), 5) Following effect and mono-flock preference (psychological). It was observed that until the rice plant around the winter roost is cut rather extensively, this roost had no value other than a part of the feeding ground, because a flock feeding at a fruit tree within that roost flew off in the evening to other roost used in this season (summer). When the rice plant at the feeding ground of the breeding area become fully grown, the flock moved north to the vegetable fields and changed the roost. This change of feeding ground and roosting place seems to be directly correlated, rather than secondarily determined by the distance of old and new roosts from the new feeding ground. A suggestive case was encountered in which a typhoon might have caused the change of roost, and human persevierance should also become a cause. The attachment of next-boxes near the spring roost has apparently given a "special attraction" to the starlings, because this roost was maintained in the second year until summer, the season in which they used to abandon that roost in the previous years. This resulted the overpopulation at this roost and by "flooding effect" the flock was splitted into two, each thereafter roosting at two new roosts about 4km. apart. In this case, the original roost was perfectly abandoned showing their mono-flock preference. In splitting up the flock they gradually established new roosts by following the others and some confusion was observed, especially in young birds, in their behaviour of undecision (an usual behaviour in changing the roost). They start to a roost but soon circle back, or swing to the direction of the other roost or sometimes take a zigzag course between the two destinations, while the "back flight" from the roost where they have just arrived was often observed.
An additional note on the feeding behaviour is given. In autumn, sparrows and starlings gather together at rice paddies, but eat different foods. Especially, the starlings search for rice worms from cut stems both remaining on the ground and hung from the poles.

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