Abstract
The foraging activity rhythm of the Grey Heron was observed in Ashizaki Bay, an estuarine habitat, and at Mawarizeki Reservoir, a non-tidal habitat, both in Aomori Prefecture. In Ashizaki Bay, herons foraged while the water level was low, although the tidal range was about 70 cm on spring tide. Herons foraged also during the nighttime low tide. In non-tidal habitat, on the other hand, they foraged constantly throughout the daytime. Herons foraged on fish using "walking slowly" tactics in Ashizaki Bay, whereas they foraged using "stand-and-wait" tactics at Mawarizeki Reservoir. This difference was thought to be attributable to the difference in main prey item (demersal fish species in Ashizaki Bay vs. pelagic fish at Mawarizeki Reservoir) and/or difference in prey catching rate (high rate in Ashizaki Bay vs. low rate at Mawarizeki).
