She saw Pete’s back arch peculiarly, and it took her a second to interpret the odd posture. He was drawing back an arrow across a bow. It flew almost straight up into the treetops, then fell back at its stilted angle, bouncing and coming to rest in the limbs fifteen feet above their heads. Dellarobia knew there was a bow-hunting season for deer but could think of no tree-dwelling creature they might want to shoot. She watched for a long while, disinclined to show herself. Vern and the others watched too, she noticed, each time Pete let an arrow fly. He was retrieving it by means of some sort of filament she couldn’t see. Fishing line, maybe. Every pass of the arrow through branches disturbed the roosting colony, sometimes causing small clumps of butterflies to drop to the ground, but this was evidently not the goal. She gathered he was trying to pass a line over the top of a tall fir tree. On the fifth try she witnessed, the arrow cleared and a whooping cheer rang out as if he’d made a touchdown. Boys.

She took the opportunity of their distraction to enter the group without direct salutation from the boss. Her anxiety since Saturday had condensed around the moment when she would meet his eyes and learn in a flash if he knew he’d been seen, yes or no. Nakedness again, of a kind. Avoiding that moment now felt crucial. She walked directly to Vern, who had begun trying to unloop the long nylon tape measure and was openly relieved to see her. Dr. Byron wanted them to census the butterflies on the ground, he told her, and they were clueless. She could well imagine how that had gone, Ovid confidently pummeling them with a flurry of unretainable instructions and walking off. Luckily she knew this one—it was the first task she’d done up here, with Bonnie and Mako. She aimed Vern north to walk the length of the site, stretching the tape as he went, and laid out one-meter squares along the transect. Pete came over to greet her.

“Did you remember the pillowcases?” His face suggested doubt, so she was thrilled to unzip her shoulder bag and draw them out one at a time like a magician’s scarves. The number, four, seemed to please him too. Pete directed the helpers to scoop all the butterflies from four of their square-meter quadrats into pillowcases after they’d counted them. “Dead or alive,” he told Vern. “One quadrat per pillowcase, doesn’t matter which ones you choose, and we’ll take them back to the lab.”

The boys went to work on their assigned plots, accepting the strange assignment without question. She recalled her own first days spent here with a tight lid on her normal curiosity, afraid of betraying her expansive ignorance. These kids were even more earnest than she’d been, judging by the way they pressed their knees into the soggy black leaf mold, all of them mindless of their jeans, which would never recover. Except Roger, who wore shorts in all weathers. Roger and Carlos were two of the three Californians who’d introduced themselves to Dellarobia when they arrived. They’d camped up here ever since, increasingly unkempt but uncomplaining. The third one had gone home. Pete called them “the Three-Fifty guys” instead of using their names, and she wondered if that was meant to be disparaging. She and Pete seemed allied, now that other people had come onto his turf, and it fascinated her, the rules of the club. She was a little seduced by the chance to be an insider, and invented the code name Sideburn Vern for Pete’s amusement. But she felt bad about it after Vern turned out to be such an eager worker. And she really liked the California boys, who were unfailingly sweet and respectful, unlike a lot of the tourists who tramped through here, demanding water and directions from Dellarobia as if she were a hired hand. If they conversed with her at all, their syllables would sometimes broaden as if she might need help with English.

She ran to catch up with Pete. “What’s the deal with the bow and arrow?” she asked him. “I could report you for shooting butterflies out of season.”

He smiled. “We’re stringing up the eye-buttons.”

“Eyes?”

“I, the letter. Little i, big B.” He opened an equipment pack and extracted a ziplock full of dime-size silver discs, like watch batteries but thicker. iButtons were tiny computerized devices that recorded temperatures over the course of time. A Velcro attachment was used to anchor each button inside a short length of PVC pipe to shelter it from rain and sun, and these would get fastened to the fishing line he’d shot over the tree. They would run them up the flagpole, so to speak, at intervals of every five meters from earth to treetops. “They save data in real time,” he explained, “like the black box in your car engine.” He also told her, though she didn’t ask, the buttons cost ten dollars each.

If her station wagon had a black box, it was news to Dellarobia, but she got the gist and went to work alongside Pete, proving adept at rigging up the housings and attaching them to the filament that would hoist them. She remembered the résumé she’d given Dovey prior to landing this job: experienced at mashing peas and arbitrating tantrums. She could now add: owns pillowcases, good at Velcro. They would leave the iButtons up the tree for forty-eight hours and then bring them back to the lab. “Weren’t you here when we did this the first time, back before Christmas?” Pete asked.

“No. I only came up with you guys just the once. We did body counts.”

“That’s right,” Pete said, contorting his mouth sideways as he tightened a knot with his straight, white teeth. Braces, she thought. Someone paid good money for those, he ought not to use them as pliers. “The temperature varies, all the way up,” he told her. “Especially in these evergreen forests. You’d be surprised. There’s a ton of temperature data recorded on the Mexican overwintering sites by Brower et al. We want to see how the thermal characteristics of the Feathertown site compare to normal roosting sites.”

She pictured these words, the Feathertown Site, appearing someday in a science book. Not the Cleary Site, or the Turnbow Site. She wondered if she was disappointed not to have her own name memorialized. That’s what it would be, a memorial, the place where a species met its demise. It was crazy, all this hard work, to that end.

“So we bring the buttons back to the lab, and then what?”

“There’s a reading device that plugs into the computer. It takes a while to download all the data and then plot it,” he warned. “Get ready for a tedious day.”

“As opposed to this one,” she said, pausing to breathe on her frozen fingers.