Sense of Direction

As a kid, I read a famous novel about two dogs and a cat that traveled some 300 miles over harsh territory to reappear at the home of their human family. “The Incredible Journey” was a work of fiction, but—as with many works of fiction—there was a nugget of truth at its center. Sometimes misplaced dogs and cats do find their way home without assistance. If we hope to comprehend this, we must start at the beginning, in the wild.

Many wild animals have exhibited a mystical connection with the earth that allowed them to navigate across long distances, hundreds or thousands of miles. Baby birds that are raised without their parents still migrate south without any adult supervision, so we know their capabilities are built-in. Sea turtles must leave their birthplace immediately after hatching to embark upon an epic journey across thousands of miles of open water. Researchers have discovered that these turtles emerge from their eggs with a built-in compass that sends them straight east. We know this because freshly-hatched turtles will consistently set out the “wrong way” when their pool is surrounded by magnets which create the illusion of an artificial North. A tiny, turtle-sized backpack magnet renders them aimless and hopelessly lost. The pigeon, world famous for his skill at homing in on a particular roof that may be over a thousand miles away, relies heavily on his sense of smell. We know this because a pigeon that can not smell can no longer find his way home. Other birds keep an eye on the sun to chart their path, calculating the precise direction it indicates with its rise and fall throughout the day. We know this because birds kept in an offset light/dark schedule for several days (much like a night shift worker) will set off precisely the “wrong way” when released back into their own time zone. Even the dung beetle, a lowly creature whose hobby is creating large pellets from animal feces (then transporting them, burying them, squabbling over them, and finally eating them), actually has his gaze fixed on the heavens when he is lost in his art. We can prove this by raising dung beetles inside a man-made planetarium.

The planet is loaded with animals that are, in various ways, more advanced than we are. Some have shared their secrets. Salmon have microscopic clusters of iron crystals (magnetite) in their skin that twist slightly, like the needle of a compass, in response to the earth’s magnetic field. This infinitesimal change sends a message to the fish’s brain, indicating what direction he is swimming. The compass mechanism within a bird’s eye is even more delicate, relying on a discrete molecule called cryptochrome to haggle over a single electron with its neighbor. This system is so sensitive that it can detect fields 3,000 times weaker than the one that shifts your compass needle. Dogs and cats could certainly be equipped with the same sort of compass, but the question remains: how do they instruct it to “find home”?

Dr. M.S. Regan