Indeed. Preoccupied with the fact that animals migrate, science was slow to approach the mystery of how they do it. Even when the migration pathways of many creatures became well documented in the 1900s, some observers continued to speculate about a mysterious “sixth sense” by which migrants divined routes.
Then, in mid-century, German scientist Gustav Kramer showed that birds use the sun as a compass. Austrian Nobel laureate Karl von Frisch discovered that honeybees take directional cues from polarized light patterns in the sky. American scientist Donald Griffin proved that bats use sound echoes to detect prey. The common thread in these finds was that animals possess sensory capabilities more varied and keener than our own.
Recent researchers, using techniques of the neurosciences, microbiology, and bioacoustics and such fundamentals of physics as electricity and magnetism, are demonstrating that the senses of the creatures of land, sea, and air are incredibly acute. Imagine:
• A homing pigeon senses changes in altitude as minute as four millimeters. Pigeons also see ultraviolet light and hear extremely low-frequency sound that emanates from wind coursing over ocean surf and mountain ranges thousands of miles distant.
• A honeybee detects infinitesimal fluctuations of the earth’s magnetic field that only the most sensitive magnetometers can measure.
• A shark recognizes an electric field on the order of five-billionths of a volt per centimeter.
• Some animals may be able to “see” the earth’s magnetic field, a proposition about as staggering as “seeing” the force of gravity.
Scientists are quick to point out, though, that the existence of a sensitivity does not prove it is used for navigation. Melvin Kreithen of the University of Pittsburgh, who discovered the homing pigeon’s remarkable sensors, says: “Detection is just the first step.” Scientists can observe the behavior of homing pigeons and infer that they use earth’s magnetic field as a reference. But then they must ask: “Where is the animal’s receptor for this information? Does the animal actually use it to navigate?” Finally, concludes Kreithen, “We must go into the field and prove how the sensitivity is used to navigate.”
As any Scout knows, a navigator needs a map and a compass. The map helps tell you where you are, and the compass indicates the direction to your destination.
But consider a steelhead in mid-Pacific, a monarch butterfly in Vermont, or an albatross released 4,000 miles from its island. What is its map and compass? What senses does it use? For those juvenile birds that migrate alone the first time, how do they know when they've arrived?
Such feats of navigation have long baffled students of animal behavior. But now scientists who ask such questions are, with ingenuity and dedication, piercing some of the veils of mystery to reveal answers that surprise and, in some cases, amaze.