Ecological study of social organization in the Great Tit, Parus major L.

IV. Pair formation and establishment of territory in the members of basic flocks

Abstract

1. This paper describes the pair formation and establishment of territory in the members of basic flock and attempts to clarify the factors determining mate selection and arrangement of territories of flock members within the basic flock range.
2. The field work was made from the spring of 1968 to the winter of 1974-75 in the Akasaka Palace, Tokyo, Japan. The study area of about 37 ha mainly consisted of mixed evergreen and deciduous broad-leaved forest. Virtually all of the birds were marked individually by colour rings and their previous history was known.
3. Pair formation took place after the basic flocks broke up in spring. Both mates of previous breeding pairs re-paired with each other as long as they survived in the following spring. As the pair-bond broke up after breeding, re-pairing of previous breeding pairs was basically not different from new pairing of widowed adults or young.
4. The members of a basic flock primarily paired with the other members of the flock. Since the domiciles of members in a basic flock overlapped extensively, it is concluded that the overlap of domiciles plays an important role in the pair formation; pair formation takes place between individuals whose domiciles overlap.
5. The pairs were spaced out with their territory after the basic flocks broke up. Most of the members in a basic flock established their territory within the basic flock range which contained all domiciles of the members. All of the adult males and most of the young males held their territory in the central part of the flock range, but some young males were forced to establish their territory in the peripheral part and a few ones were forced to disperse from their basic flock range.
6. When a more favourable area became vacant as a result of the death of the owner during autumn and winter, a surviving adult first occupied there, and then another male, usually young, established the territory in the vacant area after the adult male moved into the favourable area. When the flock contained only one adult male and the male died during winter, young male occupied the previous breeding territory of the adult male in the following spring.
7. Thus adult males dominated over young males in the establishment of territory within the basic flock range. Although the males established their territory within their domicile, the domiciles of adult and young males overlapped extensively. The adult males selected the area as domicile at least one year earlier than the young males, so the prior occupancy of adult males is important to determine the arrangement of territories within the basic flock range.
8. Therefore, it is concluded that the overlap of domiciles and the prior occupancy of an area play the important role in the social organization of the breeding season, like that of the non-breeding season in the Great Tit.