The influence of dams on avian communities within disturbed riparian habitat

Abstract

An avian community study was conducted along a 55.2 km portion of the lower Mahoning River located in western Pennsylvania and northeast Ohio, U.S.A. Low-head dams have created alternating series of free-flowing and impounded segments of water, altering the natural riverine habitat of the lower Mahoning River. The goal of this study was to examine the effects of low-head dams on the avian community and habitat structure within riparian forest. In the spring and summer of 2004, avian point counts and habitat characterization was conducted at study plots downstream and upstream of low-head dams that were at least 200 m apart (n=12). Birds were placed into habitat assemblages, as well as foraging and nesting substrate guilds. The Shannon-Weiner index (H') of diversity and the Bird Community Index (BCI) were used to evaluate avian communities in study plots. Principal Component Analysis was used to detect differences in habitat structure between study plots. At the Leavittsburg study site, the upstream study plot had a more diverse avian community than the downstream study plot. Study plots with a high H', BCI score, and percent mature forest bird species were associated with habitat more indicative of mature forest. Foraging and nesting substrate guild did not appear to be influenced by low-head dams. Oridination revealed no differences in habitat structure between study plots. Results from this study appear to indicate that the presence of low-head dams in the lower Mahoning River have a minimal effect on avian diversity. Instead, downstream and upstream study plots with high diversity and BCI scores appeared to be influenced by habitat characteristics typical of mature forest.