The breeding behaviours and territorial dispersion of Japanese Reed Bunting Emberiza yessoensis

Abstract

1. Breeding biology and territoriality of Japanese Reed Bunting Emberiza yessoensis were investigated on Kirigamine grassland, central Japan. Observations were made by means of territory mapping and time mapping methods 1961-1971 on three quadrate plots.
2. On Kirigamine grassland, the Japanese Reed Bunting is a summer breeding resident arriving in May to June and departing in September. On arrival, males gather in small flocks in some parts of the grassland, before the females arrive. Pairs are formed after various consorting behaviours for the first brood. They begin the nest-building for the second brood while they are feeding their first brood fledglings.
3. The clutch size of the first broods was 4.5±0.72 and that of the second broods 3.6±0.53. Both sexes feed their nestlings and fledglings. The nestling period is about eleven to twelve days. Of the pairs which raised first broods, 42.9% raised the second broods. The nest success was 56.5% in total of breeding nests, 78.6% in first broods and 14.3% in second broods.
4. Detailed observations, especially of territorial and sexual behaviour patterns were described.
5. Frequency of territorial fighting by males fluctuated seasonally showing approximate bimodal curve. The first peak of this bimodal curve tended to coincide with nest-building stage and the second one with fledgling and second nest-building stages.
6. The intensity and seasonal fluctuation of singing activities were different between mated and un-mated males. That of the former had moderate singing frequency and the bimodal curve was coincident with the seasonal fluctuation of territorial fightings. The depression between two peaks results from male's increasing feeding activity for nestlings together with the female. The second peak of singing frequency is highest in the season. The curve of singing frequency of un-mated male rises as mated males enter the stage of nest-building, and the curve is maintained at the same moderate level during incubation to nestling stages of mated males. And, the highest peak of singing frequency of un-mated male parallels with the highest peak of that of neighboring mated males.
7. The nesting site of Japanese Reed Bunting is on or near the ground in grassy area. It is mostly (74.2%) constructed on or among the base of bunched Miscanthus using its leaves.
8. Fifty-five nestlings and eight adults were banded with colour rings. The recovery rate in next breeding season was 7.9% in nestlings, 40% in adult males, and 25% in adult females. The sites of recoveries were on or near the places where they were reared or in the previous territories.
9. The size and contents of home-ranges are different between mated and un-mated males. The average territory size of mated male was 4 to 5ha, while that of un-mated male was 7ha.
10. Male's singing area tends to change with the territorial range. The size of singing area was about 2ha, both in mated and un-mated males, except in 'temporal' singer. Mated males had several concentration of singing posts in their singing area, but un-mated males did not have such concentrated singing posts. The singing posts of bachelors were loosely dispersed in their singing area. Of the concentrated singing posts of mated male, one was located near the nesting site and others were scattered along outer parts for defense against neighboring males. Mostly, the nest was situated in or on the edge of the singing area.
11. Location of territories of mated pairs do not change seasonally, but those of un-mated males do. Although the site is different by year, un-mated males establish their singing areas in spaces vacant among stable territories of mated males. These un-mated males hold their vigorous singing centers and foreward singing spots to keep contact with stable pair territories. These temporal singing locations of un-mated males change with stages of breeding and by time of day.