The Karner blue butterfly, which lost 99 percent of its population when it was protected as endangered 28 years ago, is making a dramatic comeback this summer in the Albany Pine Bush.

The quarter-sized butterfly was identified in the 1940s by novelist Vladimir Nabokov at the Pine Bush in the New York hamlet of Karner. The butterflies used to be abundant in and around Guilderland in the mid-20th Century; the males especially stood out since, when they open their wings, they display an almost electric indigo blue.

Driven to the brink of extinction by habitat loss, the species was federally listed as endangered in 1992. Local conservation efforts helped increase the Pine Bush population from a few hundred at that time to more than 3,000 in 2013 — the minimum recovery threshold established by the United States Fish and Wildlife Service.

On Tuesday, the Albany Pine Bush Preserve Commission invited local press to witness the population boom. Field ecologist and entomologist Amanda Dillon demonstrated the use of a long pole that is used at 60 pine bush sites to find the Karner blue. She said the number of Karners seen this month is unlike anything previously documented in the preserve.

Albany Pine Bush Preserve Commission Conservation Director Neil Gifford said that, in July, staff had observed three times as many Karner blue butterflies than before — “and there’s still a week-and-a-half left,” he said.

Driven by science, the commission’s programs of controlled burning, forest thinning, restoration seeding, and environmental education have helped the Karner population remain above 7,000 for the last seven years.

The preserve covers more than 3,350 acres and protects one of the best remaining inland pitch-pine scrub oak barrens in the world. The ecosystem grounded in sandy soil provides habitat for many plants and animals, including more than a fifth of the New York State-designated wildlife Species of Greatest Conservation Need.

While the current population size of the Karner blue butterfly cannot be calculated until the season has ended, staff report counting hundreds of butterflies on their surveys at sites throughout the preserve.

Butterflies could be observed mating on Tuesday, their abdomens end to end and the bright orange spots on the crests of their outer wings coming together to form a shape that looked rather like arched eyebrows.

“In a laboratory, protected from weather, predation and disease, we have seen that Karners have a high reproductive capacity, with individual females successfully producing hundreds of offspring,” said Gifford in a release from the commission. “Conditions in the wild are seldom that perfect, but every once in a while things can line up, and that’s what we believe we are witnessing in the preserve right now.”

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