Lunar Nature

By Terry Krautwurst

Look at the moon, and the last thing you think of is life. Suspended in space some 239,000 miles from Earth, it’s great for gazing at. But biologically, despite the recent discovery of water traces in shadowed craters, it’s a wasteland. Its air is unbreathable. Its temperatures are extreme: a blistering 243 degrees Fahrenheit during the month-long lunar day, followed by another month of deep-freeze night at 272 degrees below zero.

But that’s the moon on the moon. Here on Earth, life is linked to the moon in countless ways. Some are crucial: Astronomers, for example, tell us that without the moon’s stabilizing gravity, our planet would wobble erratically on its axis, creating climatic chaos. Other connections are less consequential and more reflective of our culture: moonshine, honeymoons and cows jumping over the moon. But the moon is connected to Earth’s biological life, too, in ways both literal and figurative, direct and indirect. Here are a few examples.

Moon Birds

Each spring and fall, our skies fill with the beating wings of birds making their annual migrations — a phenomenon that has intrigued scientists for millennia. Aristotle was among the first to suggest an explanation for the birds’ mysterious seasonal appearances and disappearances. Some species, he thought, simply hid themselves in the ground until spring. “Swallows, for instance, have often been found in holes, quite denuded of their feathers,” he wrote.

Eclipsing all other far-fetched migration theories, though, was the one presented in 1703 in a booklet titled Whence Come the Stork and the Turtle, the Crane and the Swallow, When They Know and Observe the Appointed Time of Their Coming. Birds, suggested the publication’s author, fly to the moon to spend the winter.

It’s a funny proposition in light of modern science, but don’t laugh too hard. For the past 100 years, counting birds “on” the moon has been one of ornithology’s most important tools for calculating how many, and in which directions, birds migrate. The technique, called “moonwatching,” uses the disc of the full moon as a backlit random sample of the night sky. Although some birds migrate during the day, the vast majority — swallows, sparrows, herons, warblers, flycatchers, nuthatches, wrens, orioles and most others — make the trip at night.

Around the turn of the 20th century, astronomers using telescopes noticed that birds flying in front of a bright, full moon cast clearly discernible silhouettes. By counting the number of birds passing across the moon’s face in a given amount of time, and extrapolating that number based on the size of the full moon relative to the whole sky, scientists can calculate a fair approximation of the total numbers of birds traveling during a given period.

Today, radar is the primary data-gathering tool for studying night-migrating birds. Moonwatching is still used, too, often in conjunction with sophisticated radar and infrared sensors. Tech-equipped moonwatchers can not only count birds, but also can determine their distance, altitude, size and — in some cases — species.

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