Piscivorous, colonizing birds can often be well-positioned to take advantage of migrating fish populations, especially at or around hydropower dams or other anthropogenic structures. In North American and Europe, common avian predators include the Caspian tern, the California gull, and the great blue heron.
Avian predation has been suspected to be a significant contributor to loss in migrating juvenile salmon populations. Because of this, and the fact that the potential impact to migrating salmonids is unclear, scientists and engineers at HTI set out to use acoustic telemetry combined with PIT tag technology to help better understand avian consumption.
Here are a couple examples of illustrating the need to better quantify avian predation on salmonid, and other threatened species, as well as how the combination tag was created to help quantify those impacts: