River ecosystems recovers fast after dam removal

While constructing a river dam may destroy the habitat of birds and other creatures that depend on that river for their survival, removing the dam rebounds the ecosystem much faster than expected, new research has found.

The researchers studied the American dipper, a bird set apart by its unusual feeding style.

Dippers, which are equipped with a transparent second eyelid, dive below the river's surface and walk the riverbed scouring the rocky floor for meals, mostly aquatic insects in their larval stage. They also eat some small fish, including juvenile salmon when they are available.

Dippers that are faring well point to a strong ecosystem in and around the river.

"These birds are right where aquatic and terrestrial ecosystems meet," said lead researcher Christopher Tonra, assistant professor of avian wildlife ecology at The Ohio State University in the US.

The researchers spent four years in Washington's Olympic National Park and surrounding lands. The Elwha River winds through the park and is the site of the largest dam removal in history, the study said.

Crews started tearing down the Elwha and Glines Canyon dams in 2011 and concluded in 2014, freeing the path for migratory fish for the first time in a century.

Within a year of the Elwha Dam removal, Tonra and his colleagues were able to document an increase in salmon-derived nutrients in American dippers.

Tonra was surprised, and delighted, by how quickly the salmon returned.

"It was pretty much as soon as the first dam came out and fish were beating up against the second, wanting to go," Tonra noted.

"That these rivers can come back within our own generation is a really exciting thing," Tonra said.

The findings appeared in the journal Biological Conservation.