A study of annual cycle of population size, habitat selection and activity in Japanese Chloris sinica

Abstract

1. During August 1966 and August 1968, fluctuation of population size, seasonal and daily changes of habitat use and activity loci of Chloris sinica minor were studied along Chikuma River in Nagano Prefecture, by means of line transects, repeated census and local all-day observation, as well as banding of 1, 114 individuals.2. Total number of individuals had two seasonal peaks: one the post-breeding increase of June to September (In August 1967, 48 birds, 2.4 times of April number), the other the increase of November to March due to northern migrant immigration (Peaks were 84 birds, 4.4 times of April number in the 1st year, and 125 birds, 7.0 times of April number in the 2nd year). In breeding season, May to June, the number was lowest but stable between 14-18 breeding adults. In the second year, average total number was 1.6 times higher than in the previous year.3. The annual life cycle could be divided into six periods, which are as follows:a. Scattered spring phase (April-July): The breeding season with lowest number of individuals, scattered by pairs and not gathering into flock. The village is used as nesting and farmlands as feeding areas. Relatively high rates in arboreal and aerial activities.b. Localized summer phase (July-September): Population increases by fledged young birds. Families scatter over river-side and farmlands, gradually forming local compound groups and move to river-side areas. The rate of feeding activity and the time spent on grasses are increased. Locally flocks of young birds are formed.c. Concentrated autumn phase (September-October): The local compound family groups become concentrated to form a big 'molting flock' of up to 150 birds at a certain river-side place where seed production of grasses is at its hight. Thus high rates of time are spent for feeding on grass and for 'molting rests' on trees.d. Scattered autumn phase (October-November): Having completed the molting and food become exhausted in the concentrated area, the flock breaks into small parties to spread outside, some entering villages. In November, grass seeds are fallen on the ground and the rate of ground feeding increases. Part of the population moves southwards.e. Unstable winter phase (November-February): The population increases to the annual maximum by immigrant flocks from the north and is locally unstable. They concentrate on riverside, with high rates of ground activity, 84-87%, and feeding, 91-94%. In February, the activity rates in village and farmlands increase.f. Unstable spring phase (March-April): The population decreases but in March sudden short-period increases are noticed reflecting arrival of passing flocks and birds of the study area return from the south. The rate of activity increases in the villages and farmlands, with decrease in river-side area. February and March are the most severe season. In March, 90.1% of activity is spent on the ground, with 93.1% of feeding activity. But, in April, these rates suddenly decrease and flocking activity changes by time of the day. In the morning they move about by singles, pairs, and small parties in the villages and farmlands, but towards afternoon they would still gather into flocks at river-side or cultivated fields.