A survey of an upland grassland bird community during breeding season

Abstract

1. A bird census was made during three breeding seasons at Kirigamine grassland plateau, Nagano in central Honshiu.
2. Two methods were adopted. One, the line transect census, was used during 1961-63 and the other, the square census in 1963 with an area of 500m².
3. The Grey-headed Bunting, Emberiza fucata, the Japanese Reed Bunting, Emberiza yessoënsis, the Black-browed Reed Warbler, Acrocephalus bistrigiceps, and the Stonechat, Saxicola torquata were main species of this grassland habitat. Although they occupied the same area, each species selected the respective niche and there were differences in nest sites and food items.
4. As the result of line transect census, the G.-h. Bunting and the Stonechat were uniformly distributed with the densities of 0.3-0.4 pairs and 0.3-0.7 pairs per 100 meters respectively. Although the densities of the B.-b. Reed Warbler were also 0.3-1.2 pairs, this species was much more patchy in distribution than the two others.
5. The B.-b. Reed Warblers were found in tall grass community at the lowest level and the G.-h. Buntings bordered them on both sides, while these were again bordered by the Stonechats with some overlap. The Jap. Reed Bunting was most local in distribution along the line transect.
6. In the square census, the G.-h. Bunting occurred over the whole study area and the occurrence rates of the other three species, Stonechat, B.-b. Reed Warbler and Jap. Reed Bunting, were below 50%. The Stonechat and the B.-b. Reed Warbler were found localized in somewhat colonial condition on the slopy part and at the tall grass community respectively.
7. The 'specific occupied area' was largest in the Jap. Reed Bunting, decreasing in the G.-h. Bunting, the Stonechat to the B.-h. Reed Warbler.
8. The Jap. Reed Bunting and the G.-h. Bunting similarly selected the nest site at the root of grasses, the Stonechat at a hollow of the ground with some covering, while the B.-b. Reed Warbler nested at 20-50cm above the ground in taller grasses.
9. The breeding seasons in 1963 advanced with the order of Stonechat-Jap. Reed Bunting-G.-h. Bunting-B.-h. Reed Warbler.
10. All the species took Lepidoptera larvae for chicks; many adult Diptera were fed by Stonechats and the Jap. Reed Bunting selected adult Lepidoptera, Orthoptera and spiders, while the B.-b. Reed Warbler preferred the Orthoptera.
11. Thus, the structure of bird community in this grassland consisted of the Jap. Reed Bunting and G.-h. Bunting preferring the short grass, the Stonechat of abandoned habitat and the B.-b. Reed Warbler restricted to the tall grass.