Why animals don’t get lost
Some of the most mindblowing avian migrations involve 50,000 miles of travel per annum. The New Yorker highlights a book on this subject: “…stories of these avian travellers are told in abundance in Scott Weidensaul’s “A World on the Wing: The Global Odyssey of Migratory Birds.” An ardent ornithologist, Weidensaul sometimes shares a few too many details about a few too many species, but one sympathizes: virtually every bird in the book does book-worthy things. Consider the bar-headed goose, which migrates every year from central Asia to lowland India, at elevations that rival those of commercial airplanes; in 1953, when Tenzing Norgay and Edmund Hillary made the first ascent of Mt. Everest, a member of their team looked up from the slopes and watched bar-headed geese fly over the summit. Or consider the Arctic tern, which has a taste for the poles that would put even Shackleton to shame; it lays its eggs in the Far North but winters on the Antarctic coast, yielding annual travels that can exceed fifty thousand miles. That makes the four-thousand-mile migration of the rufous hummingbird seem unimpressive by comparison, until you realize that this particular commuter weighs only around a tenth of an ounce….”
Over the last 30 years technological advances have allowed us to collect lots of data on migratory creatures. Several books have been published on this subject now. “Two main lessons emerge from those books—one tantalizing, one tragic. The first is that, although we are developing a clearer picture of where animals go, we still have a lot to learn about how they find their way. The second is that the creatures with a credible claim to being the worst navigators on the planet have steadily reduced the odds of all the others getting where they need to go, by interfering with their trajectories, impairing their route-finding abilities, and despoiling their destinations. Those feckless creatures are us, of course.”
So how do birds & animals achieve these incredible feats? “The Goulds, in “Nature’s Compass,” outline several common strategies for staying on course. These include taxis (instinctively moving directly toward or directly away from a given cue, such as light, in the case of phototaxis, or sound, in the case of phonotaxis); piloting (heading toward landmarks); compass orientation (maintaining a constant bearing in one direction); vector navigation (stringing together a sequence of compass orientations—say, heading south and then south-southwest and then due west, each for a specified distance); and dead reckoning (calculating a location based on bearing, speed, and how much time has elapsed since leaving a prior location). Each of these strategies requires one or more biological mechanisms, which is where the science of animal navigation gets interesting—because, to have a sense of direction, a given species might also need to have, among other faculties, something like a compass, something like a map, a decent memory, the ability to keep track of time, and an information-rich awareness of its environment.
The easiest of these mechanisms to understand are those that most closely resemble our own. Most humans, for instance, routinely navigate based on a combination of vision and memory, and we are not alone. One scientist, puzzled to find that his well-trained rats no longer knew their way around a maze after he moved it across his lab, eventually determined that they had been navigating via landmarks on the ceiling….
Many animals, however, navigate using senses alien to us. Pigeons, whales, and giraffes, among others, can detect infrasound—low-frequency sound waves that travel hundreds of miles in air and even farther in water. Eels and sharks can sense electric fields and find their way around underwater via electric signatures.”
Even more striking are a range of creatures who are capable of “true navigation” i.e. navigation without any reference to physical landmarks. How exactly these creatures do it is still a mystery to scientists.