Woodland Park Zoo Wildlife Conservation

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Oregon

Oregon Silverspot
Butterfly Project
In 1980, the Oregon silverspot butterfly was declared a federally threatened species. Conservation groups across the country have adopted many different tactics to save threatened or endangered species, ranging from habitat protection to comprehensive public education programs. However, in the case of the Oregon silverspot butterfly, the exact cause of its decline is unknown. Consequently, adopting a conservation plan without this knowledge would probably be a waste of time and resources. This project, which began in 1999 as a partnership between the Oregon Zoo and Lewis and Clark College, attempts to rear silver spot butterflies in captivity and then release them into the wild. This process, known as "headstarting," stabilizes the population while scientists attempt to pinpoint factors negatively affecting the butterfly.

Headstarting the Silverspot
The headstarting has proven extremely successful; a wild butterfly census taken in September 2000 showed a population of 80 butterflies, as opposed to fifty the previous year. By increasing population numbers to this level, efficient monitoring can take place, and the species will not become extinct while attempts to understand and reverse declining trends are undertaken.

In 1999, the U.S. Fish and Wildlife Service revised a recovery plan for the silverspot and, in partnership with Oregon Zoo and Lewis and Clark College, began a captive rearing and release program at Cascade Head Preserve in Oregon. This site with still abundant patches of violets, was established by The Nature Conservancy. Now WPZ is also directly aiding the effort by headstarting silverspots here at the zoo, a process similar in some ways to our long-standing western pond turtle headstart program.

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Growing the Population
Population augmentation is a complicated process, and Woodland Park Zoo participates directly in this project by rearing the butterflies in Zoo facilities. In September, adult female butterflies are captured from the population at Cascade Head, OR, and transferred to WPZ. Eggs are laid and then subsequently hatched. The newly emerged caterpillars are hydrated and fed, and placed in a laboratory setting that induces diapause (a period of no growth or development). During the winter, the Zoo's horticultural staff grows early blue violet, the butterfly's host plant. The larvae continue in diapause from September until May, when they are raised upon violet leaves by zookeepers. The caterpillars grow larger and larger until they pupate, and the pupae are returned to the site of the wild population at Cascade Head. They are released between June and September, and the adults will emerge, mate, and renew their reproductive cycle.

Preserving a Vital Habitat
The butterfly ranges from Washington south to Northern California, occurring in isolated small populations within grassland habitat in association with its host plant, the early blue violet. While WPZ is directly involved in rearing the butterflies in captivity, population augmentation is but one part of this project. Using mowing and controlled burning techniques, project ecologists attempt to increase the quality of habitat for the butterfly. Most importantly, project scientists are closely monitoring the butterfly in order to better understand its problems. In the future, scientist may attempt to reintroduce the Oregon silver spot butterfly to Washington's Long Beach Peninsula, where a historic population once existed. Woodland Park Zoo is currently experimenting with rearing techniques in the hopes of reducing mortality at all stages and developing more efficient techniques for raising larvae. This will maximize the number of pupae available for reintroduction to places such as Long Beach Peninsula.