Abstract
1. The structure and distribution of pair territories of Aegithalos caudatus in breeding season was studied. Then, the winter flock territory was discussed in comparison with them. The field studies were made at foot zone in 5 breeding seasons during 1964 and 1968. The habitat was mixed woods of middle Honshu, Japan, consisting of Quercus serrata, Castanea creata, Larix leptolepis and Pinus densifrora.
2. Breeding territorialism was discussed with analyses on pair behaviors, distribution of activity loci, movements, fighting behavior and helpers.
3. The pair formation behavior was not observed in spring but was confirmed in summer and autumn of the previous year. Pairs split from winter flock, and at interval stage of pair formation, one or several pair flocks existed. These flocks were involved within their common range of winter flock. The range of pair flock was communally defended by members of the same flock against adjacent such flocks. Pairs occur in the winter flock and gradually become isolated with each other, but never go out of the winter flock range.
4. At night, all the pairs assemble to one winter roost, but during the day each of them is engaged in nest-building at separate place. In early spring, nesting is done only in the morning, returning to flock life in the afternoon, especially when the weather is bad.
As breeding season advances, pairs remain more of the time in their own territories.
5. Pair ranges established by dividing a winter flock range are considerably overlapped, especially at their previous center of the flock. The pair of dominant male first become independent against the group of pairs of subordinate males, which settle at or near the flock center.
6. During early stage, all the pairs splitted from a common winter flock make a group and communally fight against the members of other such groups. At the stage of completion of outerwall of the nest, pairs roost in it and completely isolate themselves from the flock.
7. The highest frequency of fighting is seen in nesting period when copulation occurs, and thus the territoriality in this species becomes the most evident and its territorialism is perfectly established. After that, the fighting frequency and territory size markedly decrease.
Under such condition, the social structure settles and production of the next generation is under way. But, in reality, this stable condition is greatly disturbed by predation on their nests and various behaviors of renesting are resumed.
8. A pair has a few central areas with highest activity density which never overlap with those of adjacent pairs. The patrolling course for maintaining the pair range starts from the central area and return to it. On patrolling along the periphery of the pair range, the pair would fly against the adjacent pair when they meet.
9. The male show many available nest sites to the female who determines one of them as their nest. The male after this event performs several nest-invitation displays which remind behavior patterns of courtship and mating. The nest is not necessarily located at the central area, though in most cases it is found in or near it. Although the nest is made often in a branch of pine, typically it is concealed in a dense bush.
10. Pairs renest when the first nest is destroyed, often beyond a few adjacent pair ranges. However, the site of renesting is never selected outside of the winter flock range and tend to be correlated with the previous activity range.
11. In nestling and fledgling periods, the helpers are observed, but never before that. The helpers consist of unmated birds and unsuccessful breeding pairs. As soon as young birds become independent from the parents, the helpers and young birds make a family flock with the parent birds.
