Presence of salmon increases passerine density on Pacific Northwest streams

The annual migration of Pacific salmon (Oncorhynchus spp.) to freshwater streams and lakes provides an important nutrient subsidy to terrestrial systems in North America. We investigated the effects of salmon and other habitat variables on abundance of Winter Wren (Troglodytes troglodytes), Swainson's Thrush (Catharus ustulatus), Varied Thrush (Ixoreus naevius), Pacific-slope Flycatcher (Empidonax difficilis), Golden-crowned Kinglet (Regulus satrapa), and Chestnut-backed Chickadee (Poecile rufescens) on the central coast of British Columbia. In our comparisons of salmon-bearing and non-salmon-bearing reaches of two rivers that had waterfall barriers to salmon partway upstream, we found that position above or below the falls and proximity to the stream were the major predictors of songbird abundance. Each species, except for Chestnut-backed Chickadee, had higher densities below the falls at both rivers. Our results suggest that salmon-derived nutrients influence songbird density, and thus benefit multiple trophic levels within riparian ecosystems.