The Oregon Zoo in Portland, as part of its conservation research and intervention efforts, released native butterflies atop Mount Hebo on the Oregon Coast in early August.
The native insects were Oregon silverspot butterflies, which the zoo reared and released in an effort to boost the species’ numbers in the Northwest. Populations of the silverspots, which were once common in coastal grasslands from northern California to British Columbia, Canada, have significantly declined due to the loss of habitat and its host plant, the early blue violet.
Oregon silverspots are now listed as threatened under the U.S. Endangered Species Act.
This was the final release in a month-long effort that had zoo staff and conservation partners making weekly trips to the coast to transport butterfly pupae to grassy headlands and salt-spray meadows that comprise some of the silverspots’ last remaining habitat.
In total, nearly 450 zoo-reared silverspots were released as pupae this summer at four field sites along the Oregon Coast. At those sites, the silverspots are completing their metamorphoses inside mesh pens that protect them from voles, birds and other predators. During the next few weeks, they are expected to emerge as fully formed butterflies.
Life as fully mature silverspots, however, is brief. Adults live only about two weeks after emergence, and in that time they’ll have to mate and produce the next generation of the species.
Zoo staff said that during the final release of silverspots on Mount Hebo, they spotted a newly emerged female in the field who “fluttered straight to a nearby daisy and was joined there moments later by a male silverspot.”
“Which, you know, is the whole point,” ecologist Kaegan Scully-Engelmeyer, who managed the weekly releases and monitors the chrysalides in their release pens, for the zoo said in a statement.
The zoo began its silverspot conservation and recovery effort in 1998, but this was the first year silverspots were released at a U.S. Forest Service site atop Hebo in Tillamook County. However, Mount Hebo has long played an important role in the recovery work: Female silverspots are collected from that area and taken to the zoo’s butterfly conservation lab to lay eggs, where they can be protected and develop through winter and spring, before being released the following summer.
During the past two years, though, drought conditions have prompted additional declines among the silverspot population on Hebo. That’s because drier, hotter weather forces the early blue violet into dormancy before wild caterpillars can eat enough leaves to fully develop, resulting in fewer adults to mate and develop in the wild or be collected for the lab.
“Mount Hebo is where these pupae’s parents originally came from,” zoo conservation research associate Karen Lewis said in a statement. “Essentially, we’re putting back what we took and adding quite a few more.”
Partnering with the zoo in the conservation effort are the U.S. Fish and Wildlife Service, Seattle’s Woodland Park Zoo, Coffee Creek Correctional Facility in Wilsonville and the Institute for Applied Ecology in Corvallis.
To learn more about the effort to save Oregon silverspots and other imperiled Northwest species, go to the zoo’s website.
To read a brief summary of the status of butterfly populations worldwide, also check out an article published in Science in July 2016. (You will need a AAAS membership or access to a library with a subscription.)