For a faltering species, hope comes in the form of 450 flitting butterflies.

Researchers from the Oregon Zoo in Portland released hundreds of captive-bred silverspot butterflies to Mount Hebo last week. Conservationists hope to establish self-sustaining populations of the species, which has been threatened by habitat destruction and drought in recent years.

“It was the perfect time of year to be out there, right in the middle of the flight season,” said Karen Lewis, a conservation researcher at the Oregon Zoo, in a statement. “Adult silverspots were flying all around us and flitting across the meadows.”

Oregon silverspot butterflies were once numerous in the Pacific Northwest, their range stretching hundreds of miles into British Columbia. Habitat loss has been a major contributor to the species’ decline, but extended periods of drought may be an even bigger threat.

Adult silverspots have a lifespan of about two weeks. In that time, they have two objectives: mate, and find a patch of violets in which to lay eggs. When the larvae hatch, they will feed on the leaves of the early blue violet. But in drought conditions, the violets go dormant in order to retain nutrients. As a result, many caterpillars don’t have enough food to properly develop. Fewer adults yield fewer offspring, and so the cycle continues.

The Oregon Zoo began its recovery efforts nearly two decades ago. Every year, researchers collect female butterflies from Mount Hebo and bring them back to the zoo. The hatched larvae spend the winter in captivity, and become pupae in the spring. When summer comes around, zoo officials return the adolescent silverspots to their native habitat.

In the past month, 450 silverspot pupae have been released to various coastal locations, where they will complete their metamorphosis and emerge as adult butterflies. Lewis and colleagues are optimistic this year – already they have witnessed mating pairs along the Oregon coast.

“The goal of the recovery program is to help each population grow large enough to be self-sustaining,” Lewis said. “If it weren't for this program, three of the five remaining silverspot populations would likely be extinct.”

For big animals, the best conservation efforts often consist of three steps: restore the habitat, reintroduce the threatened animal, and keep humans as far away as possible. But the fence-it-and-forget-it method of conservation doesn’t always work for smaller animals, such as butterflies.

“Land-use planning and protection of habitat is the first thing above all,” says Travis Longcore, science director of the Los Angeles-based Urban Wildlands Group in a phone interview with The Christian Science Monitor. “But there’s a whole range of other things that might be counterintuitive to someone who is used to working with wolves or grizzly bears.”

For example, many insect larvae rely on early-successional plants for food. These types of plants sprout after a major ecosystem disturbance, such as a fire. In tightly-controlled conservation areas, this essential resource can be lost over time.

“Most butterflies are pretty specialized about what they eat,” says Jessica Hellmann, director of the University of Minnesota’s Institute on the Environment, in a phone interview with Monitor. “They can be very closely tied to particular resources or habitats, so where those resources or habitats are affected by climate change or habitat loss, the butterflies are also affected.”

The callippe silverspot, which is found along the San Francisco Bay, has been threatened by this phenomenon. In the absence of disturbance, native shrubs and trees over-colonize grasslands and choke out the butterfly’s main food source. In these cases, a more nuanced approach to conservation may be necessary.

“Conservation is frequently about reducing human disturbance,” says Dr. Longcore. “But the case might be for some butterflies that reducing disturbance can actually result in degradation of habitat. It becomes something where you have to very carefully figure out how to introduce the right amount of disturbance, although that’s not necessarily the case for the Oregon silverspot.”

As with most conservation issues, there’s no magic solution to be found here. Many projects rely on captive breeding and reintroduction, but the specifics vary significantly.

“When you get down to the finer points, it’s like with chefs,” says Longcore. “Every chef is right.”

“For lots of butterflies, effectiveness will differ based on what time of year you release, what state you release them in, and what habitat you release them to,” Dr. Hellmann says. “[Oregon Zoo researchers] seem to have found the right combination of those things. But I’d want to go back next year and see if they’re still there.”

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Captive breeding, while not an exact science, may actually be the best bet for many struggling butterfly species. They don’t always result in self-sustaining populations, but they do establish temporary populations that may survive for future captive breeding.

“When you can rear a bunch and get them going out in the wild,” says Longcore, “that’s always a great day.”