For the Birds Radio Program: Eagle Flight
Tuesday’s snow was predicted by Monday’s flight of Bald Eagles.
(Recording of a Bald Eagle)
Until this week the Northland was filled with restless little kids anxious for the first snow. The weather service kept promising it, but the skies kept holding out. By last weekend, my kids were ready to give up, resigned to a dreary and snowless November. The National Weather Service’s Dave McGinnis, who always makes the weather sound homey and interesting, was still promising snow, but I didn’t want to get their hopes up.
But then Monday morning when I looked out the window, the thin high clouds were spotted with hawks. A group of three Bald Eagles, five Red-tailed Hawks, and a Rough-legged Hawk were dancing on the light northwest wind, and I knew that winter was finally in the air. All day the eagles passed over—I was busy with my kids most of the time, but every time I went out I saw at least a couple of red-tails or an eagle. At one point a thermal carried a swirling kettle of four adult and one immature eagles, twelve Red-tails, two Rough-legs, and a handful of ravens.
Ravens seem to watch for eagles not only because it helps them to find thermals but also for the fun of harassing the enormous raptors. In my kettle the eagles circled ever upward while the ravens darted at them. Eagle wings are bigger and harder to maneuver than raven wings, and so the eagles weren’t in a good position to fight back, but, just in case, the ravens kept their distance from the lethal talons and forbidding beaks.
A thermal is just a column of warm air, which rises because it’s less dense than cool air. As the air rises away from the sunny spot on the ground where it received its heat, it cools down until it has the same density as the surrounding air. At that point the birds stream out, in search of another thermal. Each time they find one, they allow themselves to be carried up, gaining altitude effortlessly. They will lose much of this altitude before they find the next thermal, but their method minimizes the amount of energy they must expend on their southward journey. The same big wings which carry them up like so many kites are awkward and unwieldy to flap, and so over thousands of years of migration they’ve developed this wonderful pattern of flying to economize their effort.
Thermals are invisible, and so the only way a single bird finds one is to chance upon it in flight. But “eagle eyes” watch one another throughout the skies. As one eagle or hawk is carried upward on a thermal, others join it from afar, and soon they can all be seen swirling upward together. There is no more beautiful sight in the world than eagles swirling in a blue sky over your own home, unless it’s the shining eyes of little children watching these awesome birds with wonder and delight. And the promise of snow that the eagles carry on their backs makes young eyes grow even larger. Bald Eagles drag the grim final days of autumn away for good. There will still be eagles flying over through the end of the month, and even into December, but when so many of them are afloat in a November sky, winter is never far behind.
(Recording of a Bald Eagle)
This is Laura Erickson and this program has been “For the Birds.”