Navigation

Joe Meche is a member of the board of directors of the North Cascades Audubon Society and is in his ninth year as editor of the chapter newsletter. Joe is also a member of the board of directors of the Washington Brant Foundation. He has been photographing birds and landscapes for over 30 years and has been watching birds for more than 50 years.

As you read this month’s column, millions of birds are responding to generations-old instincts and preparing to migrate to their breeding grounds. Some species, like barn swallows, are already showing up in local birding hotspots. Migration is one of the truly great wonders of the natural world, but this phenomenon is much more than just a matter of moving from one place to another. Birds need a lot of fuel to make their long journeys and weather isn’t always on their side. Despite all the challenges they face, birds continue the annual procession of the species to proliferate and raise the next generation.

While we marvel at the intrinsic beauty of migration and the incomprehensible number of birds on the move, these winged wonders traverse vast expanses of open water or desert; they often migrate at night; and natural barriers such as mountain ranges stand formidably in their paths. We know that birds move across great distances every year, but how on Earth do they find their way?

We know that young birds learn from adults and that the process has been passed down through countless generations. While their navigational abilities are inborn to a great extent, young birds must also rely on experience. Many rare birds that show up in places outside their normal ranges—and cause a lot of excitement among birdwatchers—turn out to be young birds that have lost their way, or older birds that have literally been blown off course.

With birds, as it is with all animals—even humans—it’s just as important to know where they are as it is to know where they’re going. Studies have determined that birds use three primary means of navigation to find their way. These means are referred to as compasses and they are sun, star and magnetic compasses. Birds use these three compasses to establish true north.

It’s easy enough to understand the sun and star compasses, since these are things that even we can see, but the magnetic compass is a bit more difficult for us to comprehend. Birds also learn certain landmarks along their traditional migration routes, such as seashores, rivers and mountain ranges. These visual landmarks serve as useful supplements to their innate sense of direction.

The sun compass of birds works in a couple of different ways. The position of the sun is essential for orientation and birds are able to adjust their progress to compensate for the sun’s passage across the sky. Birds are also able to determine the time to migrate when the daylight hours reach a certain length. Gustav Kramer studied migratory restlessness, or zugunruhe, in Germany in the 1950s. He found that caged birds oriented to the correct direction for migration, as long as they could see the sun. On overcast days, the birds in the study showed no directional tendencies.

Birds that are nocturnal migrants rely on the stars to guide them along the way. It was once thought that the moon served as a guide for the night flyers, but when the moon is too bright, the star patterns are obscured. In a laboratory setting, birds’ abilities to orient according to the stars were studied using a planetarium. The birds always located the North Star and used it to determine the correct direction for migration.

The Earth’s geomagnetic fields comprise the equivalent of a horizontal map. Magnetic inclinations change with latitude and provide reliable information on geographical position. Recent studies confirm that birds use the Earth’s magnetic fields to define their initial compass directions and then add celestial compass information onto this foundation. Orientation by magnetic field information alone is practiced when clouds obscure celestial cues. Some, perhaps most, migratory songbirds inherit genetic programs that route them to traditional wintering grounds by controlling their orientations and flight distances.

Birds’ visual orientation is compatible with their innate sense of direction and since birds possess such superb vision, learned landmarks help to guide them on their way. The homing instinct is common in many animals but birds take it to a higher level. There are almost legendary tales of pigeons’ abilities to find their way home. Well before the advent of modern technology, carrier pigeons played an integral part in communication between units that were separated during wartime.

Birds have the ability to combine whichever navigational traits they need to find their way. Seabirds have an astounding sense of smell and have been known to “smell their way home.” Examples abound of birds finding their way home after being experimentally displaced. One particular Manx shearwater was flown to Boston and, after being released, found its way back to its nesting burrow on an island off the coast of Wales, just over twelve days later.

In their daily lives and during migration, birds travel great distances, sometimes across unfamiliar terrain. Accurate orientation is the end result of an array of diverse navigational tools that increase in sophistication with experience as the bird ages. Birds rely on acute visual memories for short-distance travel and local orientation. Birds use the positions of the sun by day and the stars by night. The solar compass compensates for the constantly changing position of the sun during the course of the day. The stellar compass does not compensate for the nightly shift of the stars, but instead focuses on the constellations close to the North Star, the fixed axis of the rotation of the night sky. And then there’s that magnetic compass!

In the historical sense, humans have only recently been able to emulate the superb navigational tools of birds. Their innate sense of direction is mostly understood, after years of research by innumerable scientists. But still, it’s difficult to imagine possessing this panoply of attributes. Of course, the ability to fly above the array of manmade obstacles certainly comes in handy.

No matter how much we study and how much we come to understand birds and how they navigate through their world—and ours—the magic will always be there. To see large flocks of birds streaming toward their breeding or wintering grounds is a sight to behold, and certainly not one to be taken for granted. I can still recall, quite vividly, one seminal Sunday morning when I was growing up. Northbound V-formations of snow geese literally filled the sky, from horizon to horizon, for almost two hours! I can still see them today. And just think, they had 3,000 miles to go but they knew exactly where they were going! §