A new one-acre island built by the U.S. Army Corps of Engineers in Malheur Lake, near Burns in southeastern Oregon, this past winter has proven to be a hit, relatively speaking, with Caspian terns.
During this spring nesting season the island has drawn, in an accounting made last week, an estimated 606 terns. Researchers report that, again as of last week, those terns have created 203 “active” nests that contain eggs or chicks.
The island was created as part of an ongoing effort to provide habitat that might attract Caspian terns. The idea is to provide habitat that will draw the fish-eating birds way from the Columbia River estuary, where they have over the past two decades established each spring and summer what is believed to the largest tern colony in the world. The colony at the estuary’s primary nesting site, East Sand Island, has averaged nearly 10,000 breeding pairs over the past decade.
The birds’ primary foodstuff in the estuary is juvenile salmon and steelhead. The primary goal of the bird relocation is to reduce predation on wild salmon and steelhead stocks that are listed under the Endangered Species Act.
The man-made Malheur Lake Island is situated in the deepest and most consistently watered area of the lake and can be used by Caspian terns as a nesting location at least nine months of the year. It has also given the terns a perfect perch from which to prey on, instead of salmon, nonnative common carp, a species that has prospered in the lake to a fault.
“They have just decimated this refuge,” according to Tim Bodeen, manager of the U.S. Fish and Wildlife Service’s 187,000 acre Malheur National Wildlife Refuge.
“They act like hogs underwater,” rooting up aquatic vegetation and creating a murky water body that has become a “biological desert,” Bodeen said.
Carp are bottom feeders and sift through mud searching for aquatic insects and plants. Feeding activities not only uproot aquatic vegetation, but also produce silt plumes in the water column which makes it difficult for plant synthesis and insect production, according to the USFWS. Carp in the 15-pound range are not uncommon in Malheur Lake and other water bodies of the refuge.
The good news is that the terns have returned in numbers, and about 80 percent of their diet has been juvenile carp.
“The majority of the forage has been carp,” Bodeen said.
The terns however “are not expected to really have much of an impact on the enormous population of carp,” said Oregon State University researcher Dan Roby. The terns are plucking off a decent number of juvenile carp, which may help to reduce future recruitment into the adult population.
Adult carp are literally too big for the terns to handle. But a swelling population of white pelicans at the refuge has been targeting the big carp. Literally thousands of the big birds – which sport the largest wing span of any Oregon bird – have been spotted at the Malheur National Wildlife Refuge in recent days, Roby said.
Roby said that he and Bodeen are hoping that the white pelicans “will help us out.”
The tern redistribution is also expected to benefit the terns by reducing the exposure of part of their population to catastrophic events such as predators, storms and disease. The East Sand Island colony in the Columbia River estuary comprises about 70 percent of the terns' western region population.
Roby said that the last known significant nesting event at Malheur was in the 1980s. And the last nesting success, until last year, was in 1991. A huge snowpack, and resulting runoff into the lake last year, raised water levels to the point that an occasional, natural island was created to provide tern habitat. Another relatively high water year this spring again created the island, which now hold about 85 breeding tern pairs, Roby said.
"Malheur Lake and other sites provide nesting habitat along the terns' natural migratory paths, leading to a more natural, dispersed population than the concentrated population on East Sand Island," Paul Schmidt, Corps’ Portland District wildlife biologist, said last fall in announcing the planned construction of the island.
Since 2009, the Corps has reduced the size of the East Sand Island nesting site by two thirds and constructed islands at Fern Ridge, Summer and Crump lakes in Oregon and Orems Unit and Sheepy and Tule lakes in California. Additional California sites are planned.
The islands already constructed have attracted more than 1,000 mating pairs of an estimated East Sand Island population of 9,000 to 10,000 pairs. The Corps estimates the redistribution project when completed will help 2.4 million to 3.1 million additional juvenile salmon survive their passage through the Columbia River estuary each year.
The Malheur Lake project is a collaborative effort between the Corps' Portland District, the USFWS’s Region 1 and the Malheur National Wildlife Refuge.
Historically, Malheur Lake was utilized by up to 35 percent of the Pacific Flyway’s canvasback duck population, was the second most important redhead production site in the West, and at its peak produced, more than 100,000 ducklings annually.
That production has been compromised by the the common carp, which became established in the lake in the 1950s. Since then the infesting carp continue to severely deplete migratory food resources and diminish water quality. The refuge now averages about 2-7 percent of its former waterfowl production capability. Also of concern is the status of native redband trout.
Efforts have been made to control the carp by chemical treatment, barriers and traps, and water management; which resulted in very short term improvements, according to the USFWS.