Caspian terns can be recruited to new colony sites (i.e., islands in Crump Lake and Summer Lake Wildlife Area) from existing breeding colonies (i.e., East Sand Island) over considerable distances, according to the preliminary conclusions of a study of Caspian tern nesting in interior Oregon and the San Francisco Bay area during 2009.
“Caspian Tern Nesting Ecology and Diet in San Francisco Bay and Interior Oregon” also preliminarily concludes that Caspian terns are more easily recruited to nest at sites with a prior history of tern nesting, as compared to sites with no history of tern nesting (i.e., Fern Ridge Reservoir west of Eugene, Ore.). The draft completed in September can be found at:
The study is part of an ongoing research project that is a joint, collaborative project between Oregon State University, Real Time Research Inc., and the USGS-Oregon Cooperative Fish and Wildlife Research Unit. Its goal is to investigate the ecology of piscivorous colonial waterbirds (primarily, Caspian terns, double-crested cormorants, American white pelicans, and several gull species) and their impacts on the survival of juvenile salmonids in the Columbia River basin and elsewhere along the Pacific Coast.
The report has been prepared for the U.S. Army Corps of Engineers, Portland District, for the purpose of assessing accomplishments of an ongoing project aimed dispersing a portion of the world’s largest Caspian tern colony, which is located at East Sand Island near the mouth of the Columbia River. A tern management plan envisions moving terns to alternative colony sites in interior Oregon and the San Francisco Bay area, as well as other locations, so that fewer of the avian predators remain in the Columbia estuary to prey on juvenile salmon and steelhead migrating toward the Pacific Ocean. Many of the young fish are members stocks that are listed under the Endangered Species Act.
East Sand was created by the Corps with the deposits of sand dredged from the main Columbia River navigation channel as part of normal maintenance. The U.S. Fish and Wildlife Service is also involved in the project in its role as a protector of migratory birds. The research is largely funded by federal entities, including the Bonneville Power Administration.
The 2009 research also showed that the diet of Caspian terns nesting at alternative colony sites identified in the USFWS’s January 2005 Final Environmental Impact Statement regarding the tern relocation project (i.e., Brooks Island, Crump Lake, and Summer Lake Wildlife Area) consisted mostly of forage fishes that are neither listed under the ESA nor of significant economic value for commercial, recreational, or subsistence fisheries.
The researchers also preliminarily conclude that:
-- the availability of suitable sites for breeding colonies was the main factor limiting the number and size of tern colonies in both the San Francisco Bay area and interior Oregon, and
-- nesting success at existing colonies was limited by attributes of those colony sites as they influenced (a) quality of nesting substrate, (b) susceptibility to mammalian and avian nest predators, (c) displacement by other colonial waterbirds, and (d) human disturbance.
As part of the project management plan the Corps completed construction of two 1-acre islands and two 0.5-acre islands at sites in interior Oregon that were in use by terns during 2009. Under the management strategy a half acre of suitable habitat at East Sand can be rendered unfit for every acre of suitable tern habitat that is created elsewhere. The goal is to reduce the East Sand colony size by two-thirds. That could mean a reduction in the amount of suitable habitat there from just under 5 acres to as little as one acre.
The new islands are specially-designed tern islands included a 1-acre island on Fern Ridge completed February 2008), a 1-acre island on Crump Lake in the Warner Valley, northeast of Lakeview, Ore, in the south-central part of the state (completed March 2008), and two 0.5-acre islands at Summer Lake Wildlife Area, also in south-central Oregon near the town of Summer Lake (completed March 2009).
Following the construction of these islands and before the arrival of Caspian terns from their wintering grounds, Caspian tern decoys and acoustic playback systems that broadcast Caspian tern calls were deployed on all the islands to attract nesting Caspian terns.
Birds banded previously for identification purposes were spotted nesting at the new interior Oregon sites and at colony sites in San Francisco Bay.