Free Thunderbird by Jack McDevitt

see that alien organisms are vastly different.” He sat back and took a deep breath. “Does that make sense?”
    â€œSparrows with fangs? That’s a bit unsettling, Michael.”
    â€œKeep your collar pulled up.”
    â€œDid you see anything there that you didn’t expect? Anything that surprised you?”
    â€œBrad, I wasn’t there long enough to do any serious research. I’d love to get invited back and spend a few weeks in that forest. Or a couple of years. I’d want to establish a laboratory outside the Cupola and bring a staff with me. But we do know a few things. I’m not the first biologist to see the place, and I had a chance to look at some of the material the others brought back.” He paused and propped his chin on one fist. “Yes, I got some surprises. On Earth, animals—all free-ranging organisms—have mitochondria. Plants, which don’t move around much, all have chloroplasts. Plants make energy from the sun, and store it as sugar molecules. Animals take the sugars from the plants and use the energy. On Eden, things aren’t so simple. Some of the birds actually have chloroplasts as well as mitochondria, which is unheard of here. As a result, the birds can glide through calm air and collect energy directly from sunlight. As far as we can tell, they can stay aloft indefinitely.
    â€œWe’ve seen a few of them go above the clouds, so they don’t care if it’s a cloudy day. They seem to have only two limitations: They can’t get enough energy to battle high winds, and they have to come down to mate and raise their young. We’ve seen them nesting in trees, and we know they eat some of the plants. And we assume they have to sleep. But we don’t know for sure.”
    Brad grinned. “I guess mating on the fly would be pretty tricky.” They both laughed. “Michael, do you think any of these animals could operate as pets? Could they blend easily with wildlife on Earth? Except, I guess, that it’s colder here. I understand it’s winter there now. So it probably doesn’t get very cold.”
    Michael leaned forward and focused on a place somewhere far from Brad. “They might blend in, but most of them couldn’t survive on Earth. The birds with the solar collectors would probably do okay though the spectrum’s a bit different. But even they need a certain amount of food. Biologies have some fundamental differences. We’re probably going to learn that the basic sugars are the same, but most of the proteins and all of the vitamins are different, as are their requirements for minerals. You and I could eat some of the fruits and grains. But except for the sugars, we wouldn’t get much nourishment. The same would be true of any Eden animals brought here. Some of the plants would do fine, though. I’d enjoy bringing back some seeds and setting up a garden.”
    â€œMichael, we’ve got some calls waiting. We’ll go to them in a couple of minutes when we get back from break.” He pressed his fingertips to the earpieces, listened to a commercial for Phil’s Jewelry Store begin, checked the time, and removed the headphones. “Brilliant, Michael,” he said.
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    J ANET CALLED EVERY morning. “Hello, Brad. Professor Fossel’s a great guest. I’d like to ask whether the animals up there reproduce more or less the way we do? The reason I’m asking is that I heard a rumor they have three sexes? Anything to that?”
    Fossel had to smother a burst of laughter. “Janet,” he said, “theoretically, the evolutionary costs of having three sexes probably make it impossible to reproduce that way. Imagine that, in order to have sex, you not only have to find one other compatible member of your species, but two—one from each of the other two genders. And you have to find them at the same time. It would make