The rare Quino checkerspot butterfly, if it is going to live on, will have to survive with a thinning layer of federal protection.

The U.S. Fish and Wildlife Service last week unveiled a new strategy for saving what was once one of the region's most abundant springtime butterflies by designating one-third as much "critical habitat" as it did in 2002. The plan was published in the Federal Register.

Once common all over Southern California, the black-and-orange-checkered butterfly now is largely restricted to Southwest Riverside County and southern San Diego County. Those are where the service is designating 62,125 acres as "critical habitat" in nine distinct units of land.

In 2002, 171,605 acres were so designated.

In response to a lawsuit filed in 2005 by home builders, asserting that the earlier decision was too broad, the service went back to the drawing board.

An environmental group strongly criticized the reduction that now has emerged from that lengthy review.

"It's a big hit," said Ileene Anderson, a biologist with the Center for Biological Diversity in Los Angeles. "It doesn't make any biological sense to do this to an animal that is already having significant problems, taking away habitat that potentially would be available for the recovery of the species."

Federal officials defended the significant rewrite of its blueprint for saving the Quino.

"We haven't taken away any habitat. It's all still there," said Jane Hendron, a spokeswoman for the Fish and Wildlife Service in Carlsbad.

It's just that large chunks of habitat now are protected by local conservation plans in Riverside and San Diego counties, and there is no longer a need in those places for a layer of federal protection, Hendron said.

She also said the service has more accurately pinpointed areas where plants could support Quino butterflies, and that has also triggered a reduction in "critical habitat."

And the service chose to leave out tribal lands in the backcountry of Riverside and San Diego counties, saying spending millions to protect the species would be too big a financial burden for Indian communities.

The reduction was celebrated by the Pacific Legal Foundation, which filed the suit on behalf of builders.

"Tens of thousands of acres were declared as critical habitat without a scientific basis for this sweeping decree," said Reed Hopper, a foundation attorney, in a statement. "We are glad the government has pulled back from a scientifically indefensible position."

Critical habitat is a designation that in many cases obligates landowners to talk to federal officials when they develop their properties, to make sure their actions won't jeopardize imperiled plants and animals. It doesn't necessarily mean land will be set aside as a reserve, though that sometimes occurs.

While the new blueprint contains significant reductions, it also contains additions in the Anza area of Riverside County. There, a new 13,880-acre unit is being designated as critical habitat to protect an emerging population of Quinos that previously wasn't seen in the area, Hendron said.

Butterflies could be migrating to the Anza area because it is higher and cooler than places nearby that Quinos have historically occupied.

"This could be the species' response to climate change," Hendron said.

The blueprint also adds an area near Campo in San Diego County where the butterfly was not previously seen.

Anderson, of the Center for Biological Diversity, termed the additions a "bright spot." Still, she said, the group expected more.

"We're looking for a much more robust designation that, instead of keeping the species in the emergency room, gets it out of there," Anderson said.

Hendron said the plan is in fact a robust one.

"It's all well and good to throw stones, but there is a great deal of science behind this designation," Hendron said.

Call staff writer Dave Downey at 760-745-6611, ext. 2623.

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Feds may slash butterfly habitat in half