Territoriality of Emberiza yessoensis in a high population density

Abstract

1. This paper deals with the structure and distribution of breeding territories of Emberiza yessoensis, under high population density. The study was conducted in May-June (6 days), 1969, on the marshy grassland along the shore of Lake Kasumi, Ibaraki, Japan.
2. Under a high breeding population density, there were two distinct areas, one the breeding colony and the other the surrounding common feeding ground. The population density in a breeding colony was 7.67 birds/ha., but if the area of the common feeding ground were added in the breeding area, it was 1.48 birds/ha.
3. The territories of a few pairs were found assembled in a group. This group formed a settling unit with nests at the central part but spaced out by actual combats of the males, whose singing activities were made at the outer part of each territory so as to protect the grouped nests and females.
4. Common feeding grounds encircled the nesting colony and each individual flew to separate feeding sites 20 to 700m apart from the nesting sites. There was no correlation in relation to flying direction even between members of a pair.
5. The breeding colony was located in a marshy grassland of Ischaemum aristatum, but the feeding sites were in weeds along paths of extensive paddy field. This can be said to be an example of a loose colony of Lack (1968).
6. The inner they settled within a colony, the smaller were their clutch size, brood size and egg weights because they needed greater distances to fly out to feeding ground with expenditure of greater energy. Thus, the resources were not shared equally by each pair.