Caspian terns are beautiful birds streamlined and elegant like fighter planes but their ravenous taste for young outward-bound salmon in the Columbia estuary has generated much ill will in the past decade.
This spring, there has been a huge turnaround in their fortunes. This has less to do with expensive efforts to limit their nesting areas on artificial islands, and much more to do with long-term efforts to restore and maintain biological diversity on the Columbia estuary.
Also facing new challenges this spring are double-crested cormorants, which share terns taste for salmon, though few would describe these miniature pterodactyls as beautiful.
Together with sea lions, seals, pikeminnows and numerous other species, terns and cormorants have long been looked upon by fishermen as rivals. As billions of dollars have been poured into salmon recovery, the Northwest Power Planning Council and others have joined the search for better balance between salmon and their principal predators.
Some salmon predators have been here virtually forever, but Caspian terns are carpetbaggers, taking advantage of manmade sediment islands and a human-related lack of eagles and other raptors that would have kept the terns in check. At East Sand Island near Chinook, terns have had an average annual (2000-09) consumption of 5.3 million juvenile salmon and steelhead, including an estimated 5.3 million last year, according to the Columbia Basin Bulletin. A total of 8,300 tern pairs nested at the island in 2010, down slightly from the 2000-10 average.
Last year, an estimated 13,600 cormorant breeding pairs nested on the island and they gobbled up about 19 million young salmon and steelhead, the Bulletin reports.
Now, decades of work to bring eagles back from the brink of extinction are yielding some surprising and beneficial results when it comes to getting terns and cormorants under control.
Harried away from their nests by eagles, the East Sand terns have left their nests open to gull predation this month. The islands cormorants have been similarly besieged by bald eagles, peregrine falcons and great horned owls.
Especially for the terns, this has meant colony collapse, with the number of active terns nests with eggs declining from about 5,000 to fewer than 500.
There will still be plenty of adult terns and cormorants around to eat migrating salmon this year. But in a longer-term perspective, this springs developments are a remarkable and gratifying example of nature returning to a kind of balance.
This is a solid endorsement of the proposition that ecosystems are vastly complex and easily thrown out of alignment. Yes, it was enormously expensive to phase out the use of DDT and other chemicals that wrecked eagle reproduction. But the advantages of our now-robust eagle population on the Lower Columbia may save a fortune in salmon-restoration funds.
We need to learn from this and take a whole-system approach to all our interactions with the natural world.