In the Pacific Northwest, we value salmon for a multitude of reasons, but the first that comes to mind may not be that they increase bird abundance and diversity. In a study completed by Marlene Wagner and John Reynolds, they found that more birds habited streams and forest ecosystems with higher salmon biomass. Along Heiltsuk First Nation land in British Columbia, Canada, they collected the composition of songbird communities and salmon influence along 14 streams over the course of two years and found that salmon are a more important predictor of bird presence than watershed size and forest composition. The most observed species in this study were the Pacific-slope flycatcher, Pacific wren, golden-crowned kinglet, and Townsend’s warbler.
Salmon provide nutrients for avian species if different ways. Some birds eat salmon and their carcasses, but some of the observed birds are migratory which means salmon may not be in their diet in the fall. Many terrestrial invertebrates feast on salmon that have spawned and then birds feast on these invertebrates. Not only do they provide a direct source of food, they also provide nitrogen to the soil which leads to higher vegetation that herbivorous insects prefer. This means salmon increase food availability and that drives number of bird species and species richness even among frugivores, generalists, and insectivores; a wonderful example of how ecosystems are connected both directly and indirectly.
Read the article here: Salmon increase forest bird abundance and diversity