Abstract
To assess the feeding site utilization by duck species in the Nomigawa River, a typical urban river in Tokyo, we conducted 32 line-transect surveys during Dec. 2008 - Apr. 2010. We also collected benthic invertebrates and grass seed samples at 11 study sites in Feb. 2010. The grass seeds was most abundant at the shallow riffle connecting to the inlet of a large pool. Meanwhile, chironomid larvae and pupae were most abundant at the shallow riffle below the outlet of a large pool. The dominant species of ducks were Anas poecilorhyncha, A. acuta and A. crecca. Main feeding sites of these three duck species were shallow riffles, but A. poecilorhyncha and A. crecca were densely congregated at the shallow riffle below the outlet of a large pool, whereas A. acuta densely congregated at the shallow riffle connecting to the inlet of a large pool. Therefore, it was supposed that the bate selectivity differs between these two groups of ducks. We suggest that the physical complexity of stream environment caused by presence or absence of artificial groundsill supports the complexity of species composition and the high density of ducks.
