Abstract
The dispersal of mated Oriental Greenfinches Carduelis sinica from "communal display" area (Nakamura 1982), the process of the establishment of territory and social organization in breeding season were investigated by detailed field observations of colour-banded individuals. Both immigration and disappearance of birds were rare cases throughout winter season and the population size of next breeding season had been determined already in the previous autumn when "communal display" ended. The pairs which did not establish their territory around the "communal display" area in autumn left one after another and established their territory at a distant site from the "communal display" area. They had an inclination to establish their territory around the territories which were established already. Therefore, the territories which were established early arround the "communal display" area formed a group of territories. On the other hand, some territories which were established later at a distance site from the area were single territory with no adjacent ones. From these facts, it was cleared that the loose colonial distribution of territories in breeding season were established through the process of dispersal from the "communal display" area. The pair bond which were established in autumn have been maintained until the next breeding season, except the death of their mate. Nest sites were changed at another sites in each renesting or second brood. In the case of renesting or second brood, new nest site was decided at the first by female and then territory was established around it. The distances were closs in the case of successful fledging and more distant in the case of failing. The changes of the nest site, however, were limited within the area close each "communal display" area. Therefore, the mixture of the members from different "communal display" area were a rare case throughout the breeding season. Each unmated male observed during the breeding season sang actively around the area where a group of territories existing. The area have a high possibility of the appearance of unmated female by the death of her mate. They excluded another unmate dmales out of their singing area. The number of unmated males increased with the progress of breeding season. Some unmated males which established their singing area at adjcent to a single territory increased with the progress. Another type of unmated males with no singing area appeared at the season when the density of unmated males was the highest. These subdominant type's unmated males intruded often into the singing area which was occupied by a dominant unmated male, and sang only when the owner were absence. From these facts, it was concluded that unmated males formed mating territories based on the dominance hierachy in breeding season. The social system of the Oriental Greenfinch and its characters were discussed.
