National Geographic : 2017 Jul
118 national geographic • July 2017 for Rhett Butler to answer, “Frankly, my dear, I don’t give a damn,” walk out the door, and disap- pear into the fog. By sloWing DoWn tiMe, scientists learn more about what happens when biology brushes up against the laws of physics. “ There’s stuff that you absolutely do not see with the naked eye,” Clark says. “Put a high-speed camera on it, and you’re like, ‘Holy cow! That’s what the bird’s doing?’” When some species spread their tails during 60-mile-an-hour dives, he says, there’s a chirping sound—not from their vocal cords but from the fluttering of tail feathers as air rushes through. In courtship displays some hummingbird spe- cies almost double their wingbeat frequency; others flap with a single wing. And when the Anna’s hummingbird pulls up after a stunt, it is subjected to roughly nine times the force of grav- ity—enough that a human fighter pilot, even one wearing a specialized G suit, could pass out. “Hummingbirds can do extraordinary things using the same building blocks found in ordinary birds,” says Doug Altshuler, a comparative phys- iologist at the University of British Columbia in Vancouver. So studying their lives can tell us a great deal about general principles of biology. On a summer morning a red glow emerges from a doorway of a room that Altshuler has taken to calling Hell. His postdoctoral research colleague, Roslyn Dakin, greets us with a sheen of sweat on her forehead. The sauna-like atmosphere is gen- erated by six LCD projectors beaming vertical stripes onto the walls of a tunnel that runs the length of the room. Inside that tunnel sits a male Anna’s hummingbird, watched from above by a panopticon of eight cameras. Dakin is trying to figure out how the birds con- trol their flight. Previous researchers theorized that flying animals have a cruise control circuit in their brains to balance movement across their field of vision. Bees do this. We do it too. When you’re driving along a wide, open highway, it feels natural to be going 70 miles an hour, but if you’re on a country road lined with trees, you’ll proba- bly tap on the brakes. Hummingbirds apparently operate under a different set of rules. In one of Dakin’s experi- ments, she has them flying through what’s es- sentially a visual treadmill. Surprisingly, they fly just as fast when vertical stripes are moving with their direction of motion as against it. At the moment we’re watching a green dot jig- gle around on the screen, an indicator that the hummingbird is sitting in the dark, doing prac- tically nothing. Periodically, he lurches halfway down the tunnel but then boomerangs back to his perch. “It’s really annoying when they don’t do exactly what you want them to do,” she says— “which is most of the time.” Dakin is convinced that hummingbirds have an instinctual wariness of larger shapes that helps them avoid collisions. Today she’s play- ing around with projecting more complicated patterns—including what looks, to my eyes, like Elvis Presley’s hair but is actually supposed to be a flower. To test this, she needs the bird to fly the length of the tunnel, which he is stubbornly refusing to do. Suddenly he lets out a chirp, and I watch the green dot flit down the tunnel, pause at the feed- er, and return. Dakin perks up; the day might not be a bust after all. She types a code for this data entry into her computer’s command prompt and hits enter. On the screen thousands of coor- dinates coalesce into a rainbow-colored piece of tinsel—a three-dimensional summary of 15 long seconds in the fast life of a hummingbird. j Once a nascent field biologist, Brendan Borrell is a freelance writer and a correspondent for Outside Mag- azine. Anand Varma is an award-winning photographer and a National Geographic Emerging Explorer. The force of flapping An Anna’s hummingbird hovers inside a special chamber at Stanford University that can instantaneously record the tiny wave of pressure generated with every wingbeat. Before Rivers Ingersoll and David Lentink designed this device, researchers had to use theories of aerodynamics to estimate the forces produced by freely flying animals.