Her heart lurched when a loud crash sounded suddenly from up the valley. Mako laughed and said it was the lumberjacks, meaning Ovid and Pete. Sometimes, he said, they climbed up trees and cut off some butterfly-filled branches, dropping them onto tarps and shaking out all the monarchs to get a count. They’d done this same kind of work last winter in Mexico. They had formulas for estimating branches per tree, trees per acre. “Counting monarchs is, like, madness,” Mako told her. “It’s like that old joke about the guy counting his herd of cows. Count the legs and divide by four.”

It didn’t seem like madness to Dellarobia, it seemed pretty methodical. And she knew the butt of that joke would be a farmer, if the person telling it said “cows” instead of “cattle.” Why was it so important to count these butterflies? She wished she could ask. Instead she said, “I just found one with a sticker on it. Is that important?”

They both whooped and came running. It was a little white dot stuck on the lower wing of one of her counted dead, something like the stickers her kids got free at the pediatrician’s. At first she’d thought it was some scrap of her own unraveling household that had fallen off her clothes. She’d been known to walk around with worse things stuck to her. But no, this dot was something official. Mako pointed out numbers on it she could barely see, a code they would key into a database in Ovid’s computer this evening. It would tell them where this butterfly had come from, where it was tagged and by whom.

“But it’s dead now,” she said, wondering how this information could help the creature in its present state. Bonnie and Mako seemed very excited about the find, putting the tagged butterfly in one of the wax-paper envelopes, and then inside a zip-sealed bag they tucked into a pocket of Bonnie’s pack.

“That’s the first tag we’ve found at this site,” Bonnie said.

“Really.” Dellarobia tried to get her mind around the idea of scientists sending messages in this way across a distance. “Where do you think it came from?”

“That’s the big question,” Bonnie said. “Could be the next state over, or it could be Ontario. God, Mako, what if it’s one of ours?” She and Mako had also done fieldwork in Canada over the summer, she explained, including tagging butterflies.

Dellarobia was floored to think of these fragile creatures owning the span of a continent, from Canada to Mexico, moving back and forth across the wide face of a land. Each one was so little and sure to die, yet they constituted a force, like an ocean tide. She was relieved Bonnie hadn’t suggested the butterflies had come straight here from Mexico. The thought of them running up here after the landslide and flood, displaced along with Josefina’s family, was a worrisome possibility she did not want to entertain. It would give her family’s mountain an air of doom. If these butterflies were refugees of a horrible misfortune, there could be no beauty in them.

As the day grew warmer they took breaks to stretch their limbs and shed their coats. Mako had to step out of his because the zipper was stuck at the bottom, the kind of thing Preston might do, which was endearing. The butterflies also began squirming around in their colonies, making for a lot of overhead action that Dellarobia found unsettling. Bonnie told her the monarchs couldn’t make their own body heat, so they were paralyzed in the cold, unable to move until the sun warmed them to 55 degrees.

“Exactly fifty-five?” Dellarobia asked. “How do you know that?”

Bonnie shrugged. “It’s been measured. It’s all published. Dr. Byron did a lot of the early work about temperatures inside and outside the clusters. They’re most protected in the interior at night, but in sunlight it’s best on the outside, so they jockey around all the time for good position.”

“Like puppies in a pile,” Dellarobia said. Rather than “pigs in a pile,” which was the actual expression. She went back to counting and finished her quadrats before the others, because they’d given her fewer of them to do. She went and sat again on the velvety green log, realizing she’d forgotten about smoking for a span of at least five minutes. Maybe eight-point-six minutes. Which made it all the worse, now that she’d remembered. If she’d had matches she would have lit up a twig, just to inhale some smoke. She lay back on the log, trying to put cigarettes out of her mind, staring up into the quivery, shifting, scaly black and orange bouquets. The clumps were massive, like great hanging bears up in the shadows. She thought of deer hunting with Cub years ago, and the way they hung up a carcass to field-butcher it. Wearing the same coat she wore now. A versatile wardrobe, suitable for all manner of dead-animal fun. The sun was trying to come out, winking behind the clouds. Wherever a ray of warm light struck the drooping tresses of butterfly clusters they would light up, butterfly wings opening wide in response, fanning slowly, drinking in warmth. Sometimes for no apparent reason a cluster seemed to break open, with butterflies spilling off it, pouring their motion into the open void. If she tried to follow any single flight through the forest air, it was impossible. They moved around so high in the trees, and there were so many, the eye jumped from one to another.

She was glad when Pete and Dr. Byron returned, even though she’d had no practical reason to miss them. Probably it was just a collie kind of thing, like Roy and Charlie, always relieved when the herd came back together. She helped spread out one of the tarps and they sat on it to eat lunch while discussing the area of the roost, the storm mortality, some things Dellarobia could understand and many she could not. She’d promised not to get in their way, but they went to some trouble now to explain things. The same transect they were sampling and counting today, they had counted a week ago, so comparing the numbers would tell how many butterflies were downed by the storm. This made sense, the matter of keeping track. She was surprised to learn the ones on the ground were not all goners. When the sun came out, a lot of them would bask and shiver to raise their body temperatures, and get going again. If the rain alone caused mortality, that would be different from what they’d seen in Mexico.

Their line of work was not just body counts, Dr. Byron assured her. Ovid. They called him that, and he was their boss, so she could try to do the same. She thought of the evening he’d come to supper and felt embarrassed all over again. But his manner with her was plain and very kind, guiding her into comprehension as he had with Preston that night. He called the butterflies a system, a “complicated system.” She was getting used to his accent. “A compli-keeted sys-tem, mon,” she would say to Dovey later, exaggerating, when she recounted all this. He’d been studying monarchs for twenty years, all over the North American continent. She asked him how long the butterflies lived, and his answer was baffling: generally about six weeks. The ones that lived through winter lasted longer, a few months, by going into something like hibernation. “Diapause,” he called it, a pause in the normal schedule of growing up, mating, and reproducing. Somewhere in midlife, the cold or darkness of winter put them all on hold, shutting down their sex drive until future notice.