Butterfly may use flowery stepping-stones.

A new study suggests that creating habitat corridors, a commonly proposed strategy for conserving species, would be the wrong approach for the rare Fender's blue butterfly. Rather than cruising down a solid highway of flowers to reach new sites, the butterflies might prefer to hopscotch between flower patches.

The Oregon butterflies live in patches of lupine flowers, but they often stray. Outside their preferred habitat, they pick up speed, moving six to eight times faster than when they meander among lupines, says ecologist Cheryl B. Schultz of the University of Washington in Seattle. Her findings indicate that, to conserve the rare butterfly, "a traditional linear corridor is inappropriate."

"It is unlikely that the butterflies would stay in a narrow corridor," she reports in the April Conservation Biology. She therefore recommends a series of "habitat stepping-stones."

Some biologists have suggested that habitat corridors are important tools for conservation. Such links would provide a thin green line connecting the remaining fragments of a once-continuous habitat. Much as cars follow interstate highways between cities, animals that are loath to leave their favorite environment would travel such botanical roadways to reach other regions of appropriate habitat.

Schultz's conclusions "call into question this dogma about corridors," says ecologist Susan Harrison of the University of California, Davis. "There's a huge unanswered question about whether corridors work.... One big lack has been careful studies of how organisms move in real, patchy environments."

Ecologist Paul Beier of Northern Arizona University in Flagstaff says there probably isn't one general answer but adds that some animals clearly need corridors. The mountain lions he studies "can't walk through industrial parks."

Schultz's motivation for the study was a proposal to create a corridor between three areas of butterfly habitat near Eugene, Ore. Although there have been other studies of butterfly populations, few focused on whether the insects will use corridors, she says (SN: 4/4/98, p. 214). "My question was, `Would a butterfly actually use a corridor if we took the time and money to create it?'"

To answer that question, Schultz chased butterflies. She and her assistants watched the insects' behavior inside areas with lupines and outside such prime habitat. The researchers dropped a small flag on the ground every time a butterfly alighted and every 20 seconds while the insect was in flight. For each flag, they recorded the time and what the butterfly was doing. On other days, the team measured how much time the butterflies spent flying.

Schultz calculated how far a Fender's blue butterfly, which is about 1.5 inches long, moves in its lifespan of about 9.5 days. When outside a lupine-rich spot, males might move as far as 2.4 kilometers and females might travel 1.7 km. A butterfly that stayed within a lupine patch would cover 1 meter or less.

Before European settlement of the prairie, Schultz says, lupine patches were probably only 0.5 km apart--plenty close for the butterflies. Now, pieces of prairie that harbor lupines are separated by 3 to 30 km. The next phase, she says, is to develop restoration techniques that will create the stepping-stones that the butterflies need.