The Thin Air Line

The laptop on the crate went ding, and Maya got to it before her aunt did.

"That's Number Eleven," Maya said. "The one you said probably died."

"The one I said probably died," her aunt agreed, not looking up from the antenna she was untangling. "Read me the altitude."

Soren leaned over Maya's shoulder. The little map showed a dot climbing a line of dots up the flank of a mountain that Soren could actually see if he turned around, white and enormous through the station window.

"Seven thousand," Soren read. "Seven thousand meters."

"Meters," Maya said. "Not feet."

"Meters," her aunt said. "Copy it into the log, would you, the good one, the paper one." She was proud of the paper one. Soren liked her immediately for that.

He wrote the number down. Then he stopped writing.

"Wait," Soren said. "How high were we this morning? When you made us stop and sit down?"

"Four thousand," said her aunt. "And you both looked like fish."

They had. Maya remembered it. Walking twenty steps and having to stand still and breathe like the air had gone thin and sneaky, like it was hiding from her on purpose.

"Four thousand made us dizzy," Maya said slowly. "And there's a goose at seven."

"Flying," said Soren. "Not sitting. Flying is the hard one. When we ran up the last bit you had to stop twice."

"So did you."

"So did I."

Maya turned around and looked at the mountain. The dot on the screen was somewhere on that white wall of it, in air so thin that her aunt kept a green metal oxygen bottle strapped by the door with a sticker that said IN CASE.

"How," said Maya. It wasn't really a question yet. It was the front of one.

Her aunt finally looked up. "That," she said, "is the correct thing to say. People have been saying it for a hundred years. Climbers up there suck on bottles and still see things that aren't there. And the goose does it with a wingspan the size of your arms."

"In how long?" Soren asked. "How long has Eleven been flying?"

Her aunt checked. "Left the wetland before dawn. So. Coming up on eight hours."

"Eight hours," Maya said. "Over the top. In one go."

Soren was chewing the end of his pen. "That can't just be practice," he said. "You can practice all you want. If there's no oxygen there's no oxygen. I couldn't practice my way up that. Nobody could. So it isn't practice. It has to be the goose. Something in the goose is different."

"Blood," said Maya.

Soren looked at her. "Why blood?"

"Because breathing gets it into your blood. That's the whole point of the fish face. You breathe and breathe and it's not getting in." Maya pressed her hand flat on her own chest. "So the goose's blood must grab it better. When there's hardly any. It grabs harder."

"Grabs harder," her aunt repeated, and now she had stopped working entirely. "Say that again."

"The stuff in blood that carries the air," Maya said. "Ours grabs it okay when there's lots. Up there there's barely any, so ours comes back empty. Theirs has to grab the little bit that's there and hold it."

"Hemoglobin," Soren said. He wrote it down. "That's the carrier. She's right, isn't she. Their hemoglobin holds on tighter."

"It does," her aunt said. "Tighter than an ordinary goose down at the lake. One tiny difference in the protein and it grips oxygen at a pressure that would leave a regular goose gasping. You two got there sitting on a crate."

Maya wasn't done. She had the look of someone counting stairs in the dark.

"But that's only half," she said. "Grabbing it out of the blood is half. You have to get it into the blood first. Out of the air. And there's hardly any air."

"Right," Soren said. "Our lungs. We breathe in, and that's the part that works, and we breathe out, and that part's just throwing the old stuff away. Out is wasted. Half of every breath is wasted." He looked at the mountain. "If I only get to use half of each breath, and there's hardly any air in the breath to start with, up there I'd be running on almost nothing."

"So the goose doesn't waste the out breath," Maya said.

They both stopped.

"Can it do that?" Maya asked her aunt. "Can something breathe out and still be getting oxygen?"

Her aunt spread her hands on the crate like she was steadying it. "Birds don't breathe the way we do," she said. "They've got air sacs behind the lungs. Air goes in a loop. Fresh air moves across the lung going one way while your blood picks it up going the other way. In, out, doesn't matter. The lung is working the whole time. Every breath, both directions."

Soren put the pen down.

"So it's not one thing," he said. "It's two. Blood that grabs the little bit that's there, and lungs that never take a break."

"Both," Maya said. "You'd need both. One without the other wouldn't get you over."

"One without the other wouldn't get you over," her aunt said. "Which is exactly why for a long time nobody believed the tracking data. A goose, doing what a jet does, on a heart you could hold in one hand."

Maya looked at the green oxygen bottle by the door. IN CASE. She looked at the dot.

"We needed a bottle to sit down at four," she said quietly. "And it's up there at seven. Right now. While we're talking."

"Right now," said her aunt.

The laptop went ding again.

Soren read it first this time. "Seven thousand two hundred," he said. His voice did something on the last number. "It's still going up."

Maya went to the window. The white wall of the mountain filled the whole square of it, and somewhere on that wall, in air that would have made her see things that weren't there, a bird the size of her two arms was climbing into it and pulling oxygen out of almost nothing on the way in and on the way out both.

Out on the sill a small brown sparrow landed, breathed its ordinary breaths, and flew off downhill toward the thick low air where the easy living was.