CHINOOK - It appears that an anticipated growth spurt in the East Sand Island Caspian tern colony has arrived. The island is just south of Chinook.
Researchers stationed in blinds recently counted roughly 22,000 terns at the lower Columbia River estuary nesting site. The count is the highest yet recorded at the colony over the course of a study that dates back to the late 1990s. The research was launched to evaluate what type of impact the avian predators have on migrating juvenile salmon.
Research leaders Ken Collis and Dan Roby caution, however, that the visual counts are, at best, estimates that are prone to error, plus or minus.
The counts are "very ballpark," Roby said. A truer measure of the colony size is that produced from low-altitude, high-resolution aerial photographs of the colony taken near the end of the egg incubation period. The photographs are used to estimate the number of breeding pairs.
Still, the overall population was expected to swell at a time when fish and wildlife managers are trying to reduce the colony size, and as a result salmon consumption, by drawing them to newly created or enhanced nesting sites outside of the estuary.
"This is a pretty good indicator that there are a lot of birds out there," Collis said of the recent count.
The birds fly north each spring to take up residence at the island and other sites. The East Sand Island tern colony is the largest known breeding colony of Caspian terns in the world.
From 2000-07 the size of the East Sand Island Caspian tern colony has been relatively stable, averaging about 9,200 breeding pairs. But population estimates jumped to 9,623 breeding pairs in 2007 and to 10,668 a year ago.
It was estimated that Caspian terns nesting on East Sand Island in 2008 ate 6.7 million juvenile salmon and steelhead. That is a higher total than in any previous year when all terns in the estuary nested on East Sand Island.
The avian predators originally settled farther upriver at an island, Rice, created with the dumping of dredge spoils from the clearing of the Columbia shipping channel. Ultimately fish and wildlife managers decided to relocate the birds by scratching out desirable nesting habitat at East Sand and covering Rice Island nesting grounds with vegetation. The idea was to locate the birds nearer the Pacific Ocean where they would have a more diverse prey base that included marine species.
The plan worked. Since 2000, the average number of smolts consumed by terns nesting on East Sand Island was 5.2 million smolts per year. That is less than half the annual consumption of juvenile salmonids by Caspian terns in the Columbia River estuary prior to 2000, when the breeding colony was located on Rice Island in the upper estuary, according to the draft 2008 season summary of the ongoing research, "Research, Monitoring, and Evaluation of Avian Predation on Salmonid Smolts in the Lower and Mid-Columbia River."
The researchers have been awaiting a population increase. They had witnessed great reproductive success in 2001, 2002 and 2003 and had expected the birds produced in those years to mature into the breeding population in as soon as three years. Now, based on study observations, the researchers conclude that the age of first reproduction is more likely five years.
"We're starting to see them come to roost," Collis said of the maturing birds that hatched out in 2001-03.
Meanwhile, terns are busy incubating eggs on specially prepared habitat at East Sand Island that has shrunk from about six acres to 3-1/2 acres. The U.S. Department of Fish and Wildlife completed an environmental impact statement, and record of decision, early in 2005 that calls for the development of habitat in Oregon and California where terns can be redistributed and a reduction in suitable habitat at East Sand Island from about six acres to 1.5 to 2 acres. It is estimated that ultimately East Sand Island would accommodate about 2,500 to 3,125 tern pairs. Two acres of suitable habitat is to be created elsewhere for every acre eliminated at East Sand.
"They're using areas outside of the area the Corps expressly prepared for them," Roby said. The Bonneville Power Administration; the U.S. Army Corps of Engineers, the USFWS, NOAA Fisheries and the Northwest Power and Conservation Council are among those supporting the research and tern relocation project.
The research project is a joint, collaborative project between Oregon State University, Real Time Research Inc., and the USGS-Oregon Cooperative Fish and Wildlife Research Unit. More information can be found at the Bird Research Northwest web site: (http://www.birdresearchnw.org/default.aspx)
With a more cramped space at East Sand terns were also trying to regain a foothold at Rice Island in vegetated habitat that has in the past been, generally, unacceptable to them. The Corps this week hired contractors to haze the terns off the site prior to egg-laying.
During the winter of 2007-2008 the U.S. Army Corps of Engineers built and/or rebuilt islands at Fern Ridge Reservoir near Eugene, Ore., and at Crump Lake in south-central Oregon. Each represents about one acre of suitable tern habitat.
Two projects were completed this past winter at the Oregon Department of Fish and Wildlife's Summer Lake Wildlife Area in central Oregon about 10 miles southeast of Bend. A half-acre site in the East Link impoundment there was built complete and a floating half-acre island was assembled at nearby Dutchy Lake.
Prior to 2008, terns had not nested at Crump Lake since 2003, when a temporary wooden platform was constructed on the submerged island and equipped with Caspian tern decoys and audio playbacks to attract nesting terns. The platform hosted 49 successful breeding pairs that year.
In 2008 a total of 428 breeding pairs colonized the rebuilt island, the largest tern colony size ever recorded at Crump Lake.
A few birds have begun to show up at the Crump and Summer lake sites, which "tend to be the latest nesting colonies," Roby said.