2015 Volume 46 Issue 2 Pages 67-81
We estimated the breeding population of Streaked Shearwaters Calonectris leucomelas, and investigated their nest burrow structures on Nakanokamishima. Streaked Shearwater nest burrows were found throughout the survey area, and at highest densities in flat or gentle sloping areas. The nest burrow density was 0.64±0.22 nest/m2 for the high nest-density area, 0.19±0.15 nest/m2 for the thicket area, and 0.10±0.10 nest/m2 for the low nest-density area. Brooding nest density was 0.13±0.10 nest/m2 for the high nest-density area, 0.01±0.03 nest/m2 for the thicket area, and 0.01±0.03 nest/m2 for the low nest-density area. We multiplied the 3D area by the nest burrow or brooding nest density in each area type, and the total numbers of nest burrow and brooding nest on Nakanokamishima were estimated to be 18,853 and 2,783 nests, respectively, and breeders as 5,566 birds. Entrances of nest burrows of Streaked Shearwater positioned in slope areas tended to be directed to downward of the slope, and entrances of those in flat places tended to be directed to the nearest coast. We found two types of nest structure: straight or curved (or hooked) types. The length of burrows was 75±22 cm for the straight type and 99±20 cm for the curved type.
