After a final trek up Saddle Mountain last week, Oregon Zoo conservationists and their partners said goodbye to 483 of the zoo’s tiniest residents.

They were releasing Oregon silverspot butterfly larvae at a select site in the coastal mountain range in an effort to save this beautiful and threatened Northwest species, which has been listed under the federal Endangered Species Act since 1980.

Once common in coastal grasslands from Northern California up into British Columbia, the silverspot remains today in just a handful of isolated populations — four of them along the Oregon Coast.

“These silverspot populations would probably be extinct if it weren’t for the recovery program,” said Kelly Gomez, who oversees the zoo’s butterfly conservation efforts. “They can only thrive in certain environments.”

Each summer, a small number of female silverspots are collected by field biologists and brought to the zoo to lay eggs. The eggs hatch into tiny caterpillars, which are kept safe during their winter dormancy. In the spring, they wake up to a leafy meal and grow quickly. When the time is right, the zoo and its conservation partners transport the silverspots to field sites for release.

The caterpillars that went out last week were the final cohort of seven this year, Gomez said. In total, nearly 2,000 Oregon Zoo–reared silverspots have been transported to field sites to bolster the remaining populations this year.

Conservationists released three groups of larvae at Saddle Mountain, where the silverspot had previously not been seen since 1972. The area was added as a reintroduction site in 2017 because a rare flower — the early blue violet — blooms in abundance there.

Early blue violets are the main food source for the silverspot caterpillars as they mature into adult butterflies, and the Oregon coastal range is one of the few remaining areas where these flowers grow in large enough quantities to sustain a butterfly population. Elsewhere, the delicate flowers have been choked out by invasive weeds and forest succession.

“The Oregon silverspots have lost a lot of their habitat,” Gomez said. “But if we continue this work, we can give them a fighting chance at survival.”

The zoo’s recovery efforts are conducted in partnership with the Oregon Parks and Recreation Department, the U.S. Fish and Wildlife Service and Seattle’s Woodland Park Zoo. The Oregon Zoo has released 35,162 Oregon silverspot butterflies since the program began in 2000.

Source: Oregon Zoo

Mark Mason