-by Juliet Berger, Ornithologist, NAP
Across Michigan and throughout the country, old, obsolete dams are being removed from rivers with a quickening pace. There are many reasons why, but the science is overwhelmingly clear that dam removal is good for fish, plants, and birds, and other wildlife.
Restoring a river corridor improves biodiversity and allows native species to flourish in the locations they’ve evolved to be over thousands of years. Experts in ecology, hydrology, and river restoration know that the change to a landscape after a dam comes out can be dramatic, but the science is overwhelmingly clear that removing a dam is good for birds. The ponds above dams are usually dominated by a single type of habitat, an open-water lake. River restoration with dam removal recovers a variety of topography and creates diverse bird habitat.
The benefits of dam removal on fish are easy to understand. Removing dams is also better overall for bird populations, but the reasons why are more nuanced. In some cases, understanding the benefits requires us to look at the landscape as a bird would.
Michigan rivers, and the Huron River specifically, are extremely segmented by dams. There are 19 dams on the main stem of the Huron River and about 100 in the watershed. Each of these dams creates some sort of pond behind it, obstructs flow, and alters the ecosystem’s natural state. Birds, such as the Prothonotary Warbler, need a natural, free-flowing river corridor, and dams damage their habitat. While bird species that thrive in flowing water struggle to find habitat and food sources, bird species that do well in flatwater have an overabundance of options. This causes an imbalance in biodiversity that stresses the entire ecosystem.
More fish, more food
Species like Bald Eagles, Great Blue Herons, and Osprey are good at adapting to a variety of riverside habitats and will continue to frequent free-flowing areas after a dam removal. This is readily observed between Ann Arbor and Dexter where Bald Eagles and Great Blue Herons are commonly found fishing the ponds above the dams and in the free-flowing stretches closer to Dexter.
Different feathers flock together
Common flatwater bird species like ducks, geese, and swans may go elsewhere after a dam removal, but there are almost always abundant options nearby for these species. Furthermore, more sensitive and reclusive species like Marsh Wrens and Virginia Rails will return to a restored area. . This can create a false sense that bird populations have declined when they are thriving. Right after a dam is removed, some people may feel saddened at not seeing some common species that they have seen for many years, but perhaps they’ll find comfort in knowing that the restored environmental conditions will continue to improve and foster returning wildlife.
As the restored impoundment area matures after a dam removal, different species of birds, even those that can be difficult to find in Michigan because they require specific niche habitats or riverside wetlands, will move back in over time. Shorebirds like Killdeer and Spotted Sandpiper often return. Herons and Kingfishers often grow in numbers. Many species of warblers use restored, natural river corridors once the area is sufficiently vegetated while Wood Ducks and Hooded Mergansers may find spots along the flowing river to call home.
What does this mean for Pen Dam?
The City of Ypsilanti, with HRWC’s support, is considering the potential effects of removing Pen Dam on wildlife. The Pen Dam impoundment occupies what could be an especially ecological beneficial stretch of river to restore. The recovered landscape will likely include many land cover types and include a mix of hills, bluffs, and floodplain meadows. That mix of land cover and topography along a swift moving stretch of river is exactly the type of habitat that has become relatively rare in southeast Michigan. With new opportunities for floodplain meadows, more Common Yellowthroats, Sedge Wrens and State Listed Species like Marsh Wren, will thrive.