Abstract
Because of its secretive habits and preference for densely vegetated habitats, there is little information on the population or distribution status of Ruddy Crakes Porzana fusca in Japan. Therefore, surveys of the wintering and breeding abundances of Ruddy Crakes were conducted in the western part of Kobe City in 2009 during January and February (winter), and again during May and June (spring). A call playback method was used during each month's surveys within suitable crake habitat at 190 survey sites in winter and 169 survey sites in spring. The study sites were classified into four habitat categories: 1) medium sized and 2) narrow streams, 3) reservoirs, and 4) agricultural land. The width of the streams were 30 to 110m in medium-sized, and 5 to 15m in narrow streams. At 190 survey sites surveyed in winter, a total of 76 crakes were detected in January, and 66 birds were detected in February. Abundances of crakes per survey site in January and February were, respectively, 0.62 and 0.62 in medium streams (N=55), 0.18 and 0.29 in narrow streams (N=49), 0.41 and 0.23 in reservoirs (N=79), and 0.14 and 0.29 in agricultural land (N=7). At 169 survey sites surveyed in spring, a total of 81 birds were detected in May, and 47 birds in were detected in June. Abundances of the crake per survey site in May and June were, respectively, 0.79 and 0.46 in medium-sized streams (N=48), 0.31 and 0.18 in narrow streams (N=49), 0.38 and 0.17 in reservoirs (N=65), and 0.38 and 0.38 in agricultural lands (N=7). Therefore, the relative abundance of crakes in medium-sized streams in both seasons was significantly greater than those of narrow streams, reservoirs, or agricultural land. In addition to medium streams, reservoirs were found to be an important habitat-type for crakes in the study area. Although there was no relationship between the reservoir size and presence of the crakes, the area of marshy plant-cover at reservoirs with crakes was significantly higher than at those reservoirs where crakes were not detected. Reservoirs where the crakes occurred had marshy plant-cover of 0.27ha (± 0.21,SD) in the winter and 0.28ha (± 0.22,SD) in the breeding season. Therefore, the reservoirs with large areas of marshy plant-cover, consisting of such vegetation as reed Phragmites australis and cattail Typha latifolia, made an important habitat for the crakes. The great abundance of crakes recorded in the study area seems to depend on the occurrence of medium sized streams and agricultural reservoirs in this region.
