Abstract
To determine the effects of substrate characteristics and macrobenthos abundance on the abundance and species richness of shorebirds, field surveys were conducted on the northern (Funabashi Sanbanse Bay Park and Yatsu-higata) and western tidal flats (upper and lower Tama River estuaries) in the inner part of Tokyo Bay, Japan, in August and September 2014, and in April, May, August and September 2015. The shorebird abundance and species richness were greater on the northern than on the western tidal flats throughout the study period, due mainly to greater species richness and abundance of two foraging groups (pause-travel and tactile-continuous) present in the northern area. The most dominant species in the pause-travel and tactile-continuous foraging groups were Pluvialis squatarola and Calidris alpina, respectively. Analyses of the relationships between the densities of both dominant species and a variety of environmental variables on the tidal flats, using generalized linear mixed models, indicated that the abundance of large, and large and small polychaetes may be the most important determinants of P. squatarola and C. alpina densities, respectively. These results suggested that the distribution pattern of shorebirds in the study area is primarily influenced by polychaete abundance.
