By Coggin Heeringa, Director, Crossroads at Big Creek
While we miss the school groups coming out to Crossroads at Big Creek for their spring field trips, we are thrilled that families are using our preserve…and it has been fun to communicate with kids online. Tim from Sturgeon Bay asks: “How do the sandhill cranes know to come back to Door County every spring?”
Knowing how to find one’s way is called “navigation.” The term comes from the Latin word meaning “ship.” Since ancient times, it has been important for sailors be able to find their way home, and birds actually use many of the same methods as sailors to navigate.
It’s not just sandhill cranes that navigate. More than a hundred species of birds leave the United States each fall. In spring, they return. Even first year birds find their way with remarkable accuracy. How do they navigate?
For years, scientists believed that a mature bird, one which had flow the route many times before, knew the lay of the land. Following topographic features like rivers, coastlines, and mountain ranges, the lead bird would escort the inexperienced birds along a “flyway” to their destination.
The explanation seemed obvious, but doubt nagged an American researcher named Donald R Griffin. Back in the 40s, he learned to fly a high-wing monoplane to follow birds, but during his early investigations, Griffin was unable to determine how birds navigate.
But in England, B.V.T Mathews discovered that though birds indeed did use landmarks, they could navigate without them. Using first homing pigeons and later wild species, he learned that bird released in unfamiliar locations found their ways home. Even when he released birds in Boston, they made it home to England. Clearly, navigation was not limited to following memorized landmarks.
Back when I was still in school, I had the privilege of meeting one the American pioneers of birds migration, Frank Bellrose. I hiked to the Bellrose laboratory on the shores of Lake Chautauqua in central Illinois.
After serving me coffee in a chipped mug that may have dated back to his first experiments, the charming gentleman described his early studies with mallards. He found that these ducks consistently head north in spring, whether released by day or night.
How, I wanted to know, could Bellrose tell which direction the birds flew if they were released at night? Chuckling, he rummaged through his office and returned with a small gizmo. “We taped these to the mallards’ legs,” he said, dropping a flashlight bulb wired to a penlight battery into my hand.
Today research has become far more sophisticated, with radar and satellite monitoring replacing flashlight bulbs and binoculars. And a number of ingenious experiments have increased our insights into bird migration.
You’ve probably used the sun as a compass. Everybody know that the sun rises in the east and sets in the west, so it is possible to get your bearings, at least roughly, by checking the position of the sun in the morning or the afternoon.
A German, Gustav Kramer first confirmed that birds use the sun as a compass, except birds of more accurate. Apparently, a biological clock exists in every bird brain. In other words, birds have an inborn awareness of time. Because they always know the precise time of day, they can adjust their orientation to the Sun in sky.
But how about the birds that migrate at night? Could they possibility use constellations? Bellrose thought so. So did a German named Franz Sauer. First, Sauer noticed that birds in outdoor cages consistency chose the right direction on starry nights, but on overcast evenings, seemed confused.
Next, in a particularly clever experiment, he put birds in a planetarium. When he projected the constellations on the domed ceiling, the birds orientated perfectly. When he rotated the images by several degrees, the birds’ orientation was a corresponding number of degrees off.
Apparently, young birds imprint on the apparent movement of the constellations around the north star. The invention of the compass certainly helped sailors navigate with more accuracy. I remember back when I was taking a course in ornithology, sitting around with my classmates speculating about bird navigation. Somebody said, “Maybe they have little compasses in their bird brains, ha, ha.”
It turns out they do! There is a little piece of iron — well, magnetite — in the bird’s beak, and there also seems to be a nerve between the beak and the brain that somehow detects the Earth’s Magnetic field. And their eyes may be able to navigate using polarized light.
So Tim, it’s kind of complicated, but birds CAN find their way home, just like sailors. The cranes are here, and the songbirds are starting to arrive, too.
It’s easy to find Crossroads at Big Creek Learning Center and Nature Preserve in Sturgeon Bay. Just turn east at the Michigan Street Roundabout and we are the first driveway on the right. Our buildings and restrooms are closed, but the trails are open, and, as always, free of charge, for all that practice social distancing and who respect our natural resources.