From December 2004 to early April in 2005, the effects of vegetated artificial islands on the habitat use of hunting Eastern Marsh Harriers Circus spilonotos, were studied at Yanaka Reservoir (ca. 450 ha), in Watarase Marsh, central Japan. The observations were conducted in four 500 × 500 m quadrats, one of which contained six artificial islands (0.1-0.32 ha). Islands were vegetated primarily with reeds (Phragmites spp.) of approximately 2.5 m in height. Another quadrat contained open water without artificial islands, and the remaining 2 quadrats contained dense reedbeds, which is an essential hunting habitat for harriers. The hunting flight frequency of the harriers in the quadrat with artificial islands was significantly higher than that with only open water. In the quadrat with artificial islands, the hunting flights per 100 × 100 m grid cells were recorded, and cells with islands had a significantly greater number of hunting flights than that of grid cells without islands. On the other hand, there was no significant difference in the hunting flight frequency between the quadrat with artificial islands and quadrats covered with reedbed. The harriers were observed to make a total of 17 hunting attempts. Of these, 76.5% occurred on the periphery of the islands, 17.6% toward the center of the islands, and 5.9% over the surface of the reservoir. These results suggest that vegetated artificial islands enhance the hunting activities of Eastern Marsh Harriers.
2005 by Japan Bird Research Association