A 24-year-old Willits woman calling herself "Warbler" has spent the past 18 days perched high in a pine tree just south of Willits.

The 60-foot tree is one of dozens marked for removal for the construction of a Highway 101 bypass around Willits.

Warbler, whose real name is Amanda Senseman, is among perhaps 100 protesters seeking to block construction because of concerns about the destruction of trees and wetlands.

"I'm not coming down unless the bypass is canceled altogether," said Senseman, a Willits-area organic farmer originally from Colorado. "I won't compromise."

Work on the bypass, which would eliminate a long-standing traffic chokepoint on the North Coast's major north-south route, is to begin at the end of the month, said Phil Frisbie, a Mendocino County Caltrans official.

"We've been fully respectful of the rights of citizens to peacefully and lawfully congregate, but she is trespassing in a construction zone," he said.

The first overt confrontation could occur next week. Caltrans on Tuesday received the final approval needed to begin construction, Frisbie said. In preparation, the agency plans to install a gate early next week to block off the area containing the tree where Senseman sits.

The protest group, called Save Little Lake Valley, is supporting Senseman's efforts by sending up meals on a pulley system and by holding weekly vigils at the site.

"It's been rather a luxurious tree sit," Senseman said. "The weather has been amazing, (although) it did rain a day and night, so it definitely motivated me to rig up my tarps better."

Tree sitting emerged as a form of environmental protest in the late 1980s. Julia "Butterfly" Hill gained international attention when she spent 738 days in a redwood tree in Humboldt County to protest clear-cutting operations. The protest ended peacefully in December 1999 in a settlement with Pacific Lumber Co.

More recently, tree sitters on the Berkeley campus delayed but ultimately failed to halt the expansion and remodeling of Memorial Stadium, a project that included removal of a stand of trees.

"While they have a right to protest, the tree sitter is a trespasser," said Mendocino County Sheriff Tom Allman.

"People do have a right to express their views, (but) if the law is being broken, we will enforce it," he said. He declined to identify the measures the department might take to evict Senseman from her new residence.

Sara Grusky, a primary organizer of the protest, said Caltrans officials and CHP officers have been driving by the site and taking pictures. "We're hopeful that we're seeing some hesitation," she said.

Grusky is part of Senseman's ground crew, a small team that uses the pulley system to send up food and dispose of waste, and keeps Senseman company.

Frisbie expressed safety concerns over Senseman's actions. "When it comes to a point where her presence is causing safety issues either for herself or our workers, we'll work with law enforcement to move her," Frisbie said. "Safety is our number one priority."

Senseman and Grusky said alternate routes could be found for the $210 million bypass. They contend that several cheaper alternative proposals by local environmental groups were ignored. They said the most viable option is a north/south corridor along Baechtel Road and Railroad Avenue west of the current proposal and closer to the city.

"There are extremely less harmful and more effective ways to solve the problem," Senseman said.

Frisbie, however, said Caltrans had looked into the Railroad Avenue corridor and found it wanting, primarily because it would require the removal of homes and would interfere with planned operation of the rail line.

Willits City Councilwoman Madge Strong is among the city's elected officials and business operators who oppose the bypass plan. She sent a letter to Sacramento lawmakers Feb. 12 requesting help in stopping it.

"It's really the 11th hour," Strong said. "But I think a lot of people who are supportive of this bypass don't realize what they're getting."

Councilman Bruce Burton said Caltrans has gone overboard accommodating environmental concerns.

"The project is really a result of Caltrans being overly sensitive," Burton said. "This project clearly reflects the input of those (environmental) agencies more than the engineering and usefulness of the design."

Businessman Pete Swanton said the current Caltrans plan will hinder businesses. "I do think there is a traffic issue, (but) the current plan, with its lack of a (Highway 20) interchange, does not benefit the town," said Swanton, who owns Main Street Music & Video and the Shanachie Pub in Willits.

In 2010, a petition opposing the bypass was signed by 120 local businesses owners, Grusky said.

Despite temperatures dropping below 30 degrees and the impending threat of eviction, Senseman said she does not plan to leave her perch anytime soon.

"I felt I had an obligation to protest," she said. "So now I'm sitting in a tree."

You can reach Staff Writer Melody Karpinski at 521-5205 or melody.karpinski@pressdemocrat.com.