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Ecological Comment: Little dipper, big science

A column from Selkirk College fish and wildlife students
(L-R) David Cox and Xesca Calderer are second year Recreation, Fish and Wildlife students at Castlegar’s Selkirk College. Photo: Submitted

If you sit for a moment beside a rocky mountain stream here in the Columbian river basin you may be joined by a small, feathered friend. Plump and grey, with a short wren-like tail, the American Dipper is a denizen of any place where cold water flows. Something about this little bird never fails to draw the eye. Perhaps it is their derring-do, as they hop from rock to rock, bobbing the body cheerfully and diving into the currents of fast-moving runs and riffles without hesitation. The American Dipper does not fear crashing white water; they were born beside it and are never found far from it.

As North America’s only aquatic songbird, American Dippers are uniquely adapted to their water loving ways. A second membranous eyelid — which you will notice as a flash of white while blinking — allows them to see and hunt underwater, and special scales in the nostrils keep water from getting in when submerged. Their song also reflects their mountain stream home, a series of high whistles and low trills, bubbling like and rising above the noise of rushing water.

Biologists and naturalists have long known that the presence of the American Dipper is a good indicator of stream health. The American Dipper’s diet is made up of those creatures who live in and amongst the sand and gravel that makes up the substrate of a stream bed: caddisfly and mayfly larva, dragonfly nymphs and fish fry are what’s on the menu.

To see an American Dipper happily hunting is to know that a stream is healthy enough to support their preferred benthic buffet. Now, as biomonitoring methods and technologies have become more refined, researchers are looking to this small bird for more of what they can tell us about the health of our waterways.

It is their role as a miniature apex predator which makes the American Dipper a good bioindicator. Testing of their eggs, feathers, feces, and blood can reveal an accumulation of minerals and toxins that may indicate potential toxicity in a water way.

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Researchers working in the Rocky Mountain foothills of Alberta found elevated, and potentially concerning, levels of selenium in the eggs of American Dippers living downstream from open-pit coal mines. In the Chilliwack River basin, it’s been found that dippers who live on the main river year-round had significantly higher levels of mercury, cadmium, copper, and other trace minerals in their feathers and feces than those dippers who lived in higher elevation mountain streams. And, on the coast of BC, researchers have been studying the potential effects that disruption of natural flow regimes by run-of-the-river dams can have on the nutritional profile of a stream by testing the blood of American Dippers. They found elevated levels of mercury in the blood of those dippers living below the study dams when compared to the control population.

The American Dipper may still have more to teach us about the health of our streams, but there is joy in simply knowing this little bird who’s not afraid to get wet. They tolerate onlookers in their hunting grounds, so long as you quietly watch.

There are many excellent places to see the American Dipper nearby: take a stroll through Millennium Park or the Waldie Island trail and keep your eyes on the rocky shore of the Columbia, or make a visit to one of it’s tributaries, such as Glade or Norn’s, Creek to see this little bird in action.

David Cox and Xesca Calderer are second year Recreation, Fish and Wildlife students at Castlegar’s Selkirk College.