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Aquatic insects are an important prey source for birds and other insects, but may also move aquatic contaminants, such as mercury, to riparian food webs.

Researchers studied riparian songbirds and common riparian arachnids from sites along the Willamette River in western Oregon, using stable isotopes to see if those that rely more on aquatic insect prey have higher mercury exposure than those that eat more terrestrial insects. Both arachnid and songbird species varied in the proportion of aquatic prey they ate, and there was a positive correlation between the amount of the aquatic prey in their diet and their mercury concentrations. Songbirds sampled earlier in the spring season, which coincides with timing of egg laying and development, consistently relied more on aquatic prey than those sampled later in the summer. While the seasonal pulse of aquatic prey to terrestrial ecosystems is an important source of nutrients to riparian species, it is also an important vector of mercury to insectivores.

Jackson, A.K., Eagles-Smith, C.A., Robinson, W.D., 2020, Differential reliance on aquatic prey subsidies influences mercury exposure in riparian arachnids and songbirds: Ecology and Evolution, online, https://doi.org/10.1002/ece3.7549.

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