If the line of caribou migration was to be established for good, and the entire zone made into a habitat corridor, then the land itself would have to be changed, as it had been before. Again humans would be altering it. All Earth was a park now, a work of art, shaped by artists. This new alteration was just one more stroke of the brush.

The transformation of taiga into cropland had been a matter of shaving down high points and filling up low points, with the growth of new topsoil hastened by engineered bacteria. Thus it was pretty flat now, as if a sea surface with a slight groundswell. But with the freeze-thaw cycle and the permafrost melt, things had been unflattening. The passage of the caribou was enough to tear up the topsoil; where they had passed, it looked like a phalanx of tractors hauling spikes had churned through the wheat. Swan avoided their track for that reason, except for brief excursions into the muck to bury transponder beacons, and also to mark the soil with scents, and herbicides aimed at wheat. They were also seeding boreal forest. In some places they were blowing up the land, tossing the blankets of introduced soil aside to bring the original taiga bacteria back to the surface. All this had to be done while the caribou were far enough away that they were not scared from coming back; but there was a lot to do, so they were starting as soon as they could.

She slept those nights in her bodysuit, which had an aerogel mattress and blanket in its pockets to keep her warm, and enough food for a few days. Once or twice she checked in with her team, but she preferred to be by herself, unwolfish though that was, to track the wolves. She seldom had the pack in sight now, but she could track them by sign; the ground was soft, the paw prints of the nine frequent. Her own Group of Nine.

On the third morning, well before dawn, after a night of little sleep, she decided to rise and catch up to the pack if she could. In the dark and cold she hiked with a headlamp on, and saw the tracks on the ground best when she took the light off her head and held it near the ground and pointing forward.

About an hour before dawn she heard their howls ahead. It was their dawn chorus. Wolves howled at the sight of Venus rising, knowing the sun would come soon after. Swan saw what they were howling at, but by its relation to Orion knew it was not Venus, but Sirius. The wolves had been fooled yet again; the Pawnee had even named Sirius He-Who-Fools-the-Wolves for this very mistake. When Venus itself rose, about half an hour later, only one uneasy lupine astronomer spoke up again to howl that something was wrong. Swan laughed to hear it. Now other wolves farther to the west would be taking up the dawn howl. For a long time when dawn crossed North America, there had been a terminator zone of howling wolves running the length of the whole continent, moving west with the day. Now that might come back.

When it was light, she worked her way closer to them by tracking that uneasy astronomer. The wolves had apparently stayed on a pingo that night, and they yipped and barked gruffly as she approached; they didn’t want to leave, and they didn’t want her to get any nearer. Something was going on up there, she thought; one of them giving birth or something like that. She waited for them at a distance, and only when they had slunk off to the east did she climb the soft side of the pingo to check it out.

A sound stopped her cold; she saw nothing at first, but there was a little pond at the very top of the pingo, a kettle like the caldera of a miniature volcano. Noise from there—a whining—she walked up to the edge of it to look down. A young wolf, fur wet and muddy, was slinking along a narrow edge of clay rimming the water three or four meters below. Walls of the hole were vertical, even hollowed out and eaten back by the water at the bottom, which had a tint of turquoise in its muddy blue, as if it might be floored by the ice at the pingo’s core. The wolf pawed at the lined clay. A young male wolf. He looked up at her and she half extended a hand toward him, and with that the ground under her gave way, and despite her twist and leap she fell into the pond with a load of mud.

The wolf barked once and cringed away from her. She swam; she had not hit the bottom of the pond, despite plunging deeply in when she fell. She swam to the other side of the wall and climbed out onto a narrow ring of exposed mud, which went all the way around. It was like being inside a vase. Her fall hole had created a spout for it.

Swan avoided looking at the wolf. She whistled and cooed like a dove, then a nightingale. She had never seen a wolf eating a bird of any kind, but just so he didn’t get any ideas, she added a short hawk’s cry. He was still trying to climb out; he was afraid of her. He fell back as the wet overhanging mud gave under his forepaws. He hit the water upside down and Swan reached out instinctively to help, but of course he was perfectly capable of twisting around and swimming back to the band of clay, and when he felt her touch he whipped around and bit her right hand, then swam desperately away. She shouted in pain and surprise. Her blood was in the water, in his mouth. The bite burned, and there was one puncture in the back of the hand that was going to well blood for a long time.

Her bodysuit, which was keeping everything but her head dry, had a first aid kit in its thigh pocket. She pulled it out and considered whether skin glue would work on a puncture wound. Well, it had to be tried. She punctured the tube and poured a lot of the glue into the dark red hole, then held a gauze pad to it hard. The gauze would be glued into the hole, but she could cut the excess away and leave the rest in there, and it would be all right.

The inner wall of the kettle was smooth except for some horizontal banding. How exactly was she going to get out? She reached into her pocket for her mobile, found that the pocket was empty. The pocket had been open, as she had been calling her colleagues pretty frequently. Well, they would notice her absence and GPS her. Possibly she could dive down to the bottom of the pond and recover the mobile, and possibly it would still be working after being submerged.

Actually neither of these seemed very likely. “Pauline, can you locate my mobile?”

“No.”

“Can you contact my team for me?”

“No. I am designed to be in contact with you alone, by way of a short-range airport function.”

“No radio?”

“No long-range radio transmitter, as you know.”

“As I shouldknow. You useless piece of crap.”

The wolf was growling, and Swan shut up. Briefly she cawed. “Hawk!” she cawed, thinking the young wolf might give her some space as a creature that spoke the crow language. She didn’t know what to do, really.

“Pauline, how can I get out of here?”

“I don’t know.” This, coming without even a slight delay, sounded faintly disapproving.

Swan moved around the circumferential band of mud, and the wolf moved with her to stay across the pond. If the higher ledges on this side held under her weight, then she might be able to climb out. She tested it, glancing at the wolf as she did. He was facing her but looking a bit to the side. It was quickly obvious that the mud of the wall was not going to hold her up. She needed sticks to carve steps, or to stick into the mud far enough to give her a hold. But the kettle had no sticks in it. Again she wondered about finding things at the bottom of the pond. But the water was frigid, and her bodysuit did not cover her head. And there was no way of telling how far down the bottom was, and whether there was anything down there anyway.

“Pauline, I’m afraid we’re stuck here.”

“Yes.”