OHSAKO Yoshito
Japanese Journal of Ornithology, 38(1) 15-29, 1989
1) Flock organization, dispersion and terriorial behaviour of the wintering Hooded Cranes Grus monacha were studied in Izumi and Akune, southwestern Kyushu from 1980 to 1984.<br>2) Most of the cranes spent the daytime at a feeding site adjacent to their roost, but about 10% of them flew out in the early morning and returned in the evening. All cranes gathered in two communal roosts at night.<br>3) A total of 83 different units (solitary birds and flocks) was observed by line censuses outside the feeding site.One solitary bird was observed(1.2%)and flocks(98.8%)ranged from two to 102birds. The flock sizes of less than ten birds in order of frequency were three(36.1%), two (16.9%), four(14.5%), six(3.6%), five(2.4%), eight(1.2%), and nine(1.2%). The two-bird flocks consisting of adults were thought to be pairs, and three-bird flocks with one juvenile and four-bird flocks with two juveniles were thought to be families. Large-size flocks consisted of solitary immature birds, solitary adults, pairs and families.<br>4) Territorial, resident and wandering units were observed outside the feeding site. In the territorial units, semi-territorial units which were subordinate to the neighbouring units but excluded other units, were observed. The territorial and resident units were pairs or families. The wandering units were solitary birds, pairs, families or mixed flocks. Excluding units which had hostility towards other units and little site attachment, were obserded at the feeding site.<br>5) Alert, threat-approaching, attacking and confronting were described as territorial behaviour. Both sexes defended their territory, while a male took the active role in direct attacks on intruders. Territory size was 54, 790 m2. One territory was kept by the same flock throughout several winters.<br>6)Immature birds and solitary adults are thought to join the mixed flocks, forming pairs with the members of the flocks. Such pairs may leave the mixed flocks to establish their own territories.<br>7) The number of territorial cranes was less than 8.4%, which is thought that cranes gathered at the feeding site and did not hold territories outside the site because the food was short. However, pair and family territories are the most stable in term of efficiency in defense when they maintain territories.