Birds in flight, and magnetite

Autumn is here. Schools are back in session, the flowers of summer are fading, and we are all breathing a sigh of relief after one of the hottest summers on record. We find ourselves busy doing fall sorts of things, wondering if this is the last time to cut the grass, or getting our leaf blowers in shape. And while we are busy with human things, nature seems busy with her own thoughts of fall. Squirrels are hoarding, fur is lengthening, and certain birds are making travel arrangements. But did you ever wonder exactly how the birds know which way it is to their favorite vacation spas?

Most bird watchers can tell you which birds stay and which birds leave for winter. They may even know the destinations of the ones that leave, perhaps even the departure and arrival dates. But how the birds know which way to go is something they’re not telling. This subject has been debated for thousands of years and while we have learned some important clues about this mystery, scientists are still speculating on some of the details.

The 4th century BC philosopher Aristotle was one of the first people to suggest that birds migrate. Aristotle seemed to have nothing better to do than decide how the heavens operated. Most of the time he was pounding his fist about how the Earth stood still, was the center of the cosmos, and everything revolved around the Earth. But now and then he turned his thoughts to other areas. Some birds, Aristotle proclaimed, migrated; others, he added, hibernated in holes in the ground.

We know that birds do not hibernate in holes. We know that our hummingbirds migrate to Central America, the Bobolinks to Argentina. We know where they go, but how do they do it? It was once thought that birds learned migration from older birds. This was discounted when young birds were captured and held until their flocks departed. Once released, the youngsters left too,- along the same path!

There is even evidence that birds navigate by the Sun, Moon and stars. In a study by Dr. Stephen T. Emlen of Cornell University, indigo buntings were kept in a planetarium. In the planetarium, day and night could be simulated. The days and nights were shortened to simulate spring migration periods. As the projection of the stars was rotated, these birds tended to go in different directions accordingly; they appeared to navigate by the north star! We can use the north star, Polaris, to ascertain latitude, distance north of the equator. The altitude of Polaris in the sky will indicate your latitude.

But birds seem to use other methods for navigating as well. There have been studies with homing pigeons where the birds were put in light proof boxes and transported to another place and released. In most cases, the birds immediately found their way home.

A recent discovery of bird navigation comes from Cornell University where William T. Keeton of Cornell discovered that pigeons (and some bees) have trace amounts of magnetite in their brain tissue. Magnetite is a compound of iron and oxygen which apparently makes the birds aware of north south magnetic orientation. Keeton released blindfolded homing pigeons which immediately found their way home. But when he released the same birds with small magnets attached to their necks, the magnets seemed to affect the birds navigational ability and the birds became disoriented.

So it seems that birds may navigate by various methods, combinations of visual, sensory and magnetic methods. Whichever methods they use, it enables these birds to navigate thousands of miles with remarkable accuracy.