Drama in an Untamed Ecosystem - Alaska's Copper River Delta - includes related article on federal and state regulations

National Wildlife, April-May, 1999 by Sharon Begley

And although these species all are threats to duskies, what Grand and Anthony found with their cameras turned up one foe in particular. They got eight shots of predators in action last spring, and in every single case the predator was an American bald eagle. At least once, the eagle also killed the mother-to-be. "Out of every 10 dusky nests, about 3 produce gos- lings," calculates Grand. "We suspect that more than half the depredation is by eagles." And that brings wildlife experts like Grand face to face with what they are calling the Dusky Dilemma: Should the U.S. Fish and Wildlife Service and other agencies charged with protecting wildlife try to control the bald eagle--America's national icon, the very symbol of wilderness--for the sake of a relatively nondescript bird that few people have even heard of? Says Russ Oates, wildlife supervisor at the U.S. Fish and Wildlife Service's Anchorage office, "It's a terrible management dilemma."

The latest aerial surveys of dusky populations suggest the bird's numbers may be plunging like the North American Plate itself. From 1961 through 1970, reports William Eldridge of the U.S. Fish and Wildlife Service's Anchorage office, aerial surveys counted an average of 18,693 duskies. That increased somewhat in the 1970s, but then came a long, slow decline. "The biggest influence on the population has been the rate of nest depredation," says Grand. "In the 1950s and 1960s, nesting success was about 80 percent." If his results are an indication of predation throughout the delta, now it's less than half that--due, in large part, to eagles. As a result, the dusky is facing extinction as what the Fish and Wildlilfe Service's Oates calls "a biologically meaningful subspecies."

Here's what seems to be happening. Eagles are attracted to the Copper River Delta by huge runs of little schooling fish called eulachon (pronounced "hooligan"). But the eagles--he has counted 50 to 80 at a time waiting along riverbeds--generally show up in Anthony and Grand's study area before the fish. So they prey on dusky nests until the fish arrive. Then, when the fish are gone, the eagles switch to goslings: "We've put transmitters on goslings and have tracked them back to eagle nests," says Grand. "In 1997 and 1998, we attributed about one-quarter of gosling mortality to eagles." With goslings not growing up to reproduce, the breeding population of duskies is falling 2 to 4 percent a year, estimates Grand.

The options available to wildlife managers are dwindling. Since 1983 the Forest Service has built 861 artificial nesting islands, of six designs, in the delta. In the most popular model, floating fiberglass squares measuring about 5 feet on each side are anchored in some of the delta's larger ponds. "Nesting success is higher on the islands," says Grand. The biologists don't know why, except that mammalian predators can't reach the islands easily and eagles may not like the islands' small size and tendency to bob in the water.

Further restrictions on hunting aren't going to be popular. As it is, the dusky quota in Oregon and Washington is only 300 birds per season (November through early March), and "all of the quota is reserved for mistakes," says Fish and Wildlife Service biologist Robert Trost. In other words, hunters are not allowed to target duskies. To get a license a hunter has to pass a course that teaches the difficult task of distinguishing a dusky from other subspecies that winter in the Willamette and lower Columbia River valleys; the license of any hunter who nails a dusky by mistake is pulled for the season.