Abstract
(1) Breeding habit, home range, territory and seasonal changes of a population of the Brown Dipper Cinclus pallasii were investigated from March 1980 to August 1982, along the upper reaches of the Tokachi river system, in south-central Hokkaido.
(2) Dippers breed once a year. Pairing starts in early February. Home ranges are established first, then territories are formed within the home ranges. Nest construction begins from the middle of April. Clutch size is 4-5 (mean 4.7), and eggs start hatching from the middle of May. The incubation period was not ascertained. The fledgling period was of 21 days. Breeding success was 25%, and seemed to be dependent on predation.
(3) The young remain with their parents after fledgling, unitl the parent birds start molting in July when the family disperses.
(4) Dippers are strongly attached to their breeding area and 58.8% returned to the same places.17.7% of individuals birds came back every year for three years, but none were observed to come back for four successive years.
(5) The average home range length was 904±88 meters.
(6) Territories formed on average 81% of the home ranges.
(7) Estimations of Brown Dipper population by the line census and the simultaneous surveys gave similar results.
(8) The environmental assessment was made on the basis of feeding types, feeding frequencies, and type of river-bed. Home range length (size) tended to be shorter where the environmental index was higher.
(9) The Brown Dipper numbers showed seasonal changes. A maximum population was usually reached in the breeding season, and the number of birds decreased with fledgling of the young due to the post-breeding movement of the population. However, there was an increase of birds from summer to autumn. Winter numbers depended on the severity of the winter, in some years birds left the area completely. Numbers increased again towards the pairing season in February.
