Wonders of Bird Migration
By Lisa Hug
September is a month when many birds are exiting cold northern latitudes and migrating to warmer and more food-rich southern areas. Bird migration is one of those marvels of nature that never stops fascinating us.
How do the birds know where to go, when to leave, how high to fly, or even when to stop? And, how can they go thousands of miles in one stretch without stopping to eat or rest? We can watch them; we can read books and scientific papers on bird migration and memorize all the facts and statistics. But, in the end, we come back to the same question:
How on earth can they possibly do what they do?
There is a bird passing by Sonoma County right now that is in the middle of the longest journey known in the animal kingdom. This is the Arctic Tern. Most of us won’t see it, and won’t even be aware of it. But, at this moment, hundreds are flying southward just a few miles offshore from Bodega Head. They are flying from the Arctic Regions of Alaska and Canada to Antarctica. The Arctic Tern weighs about 4 ounces and has about a 2 and a half foot wingspan. This small bird lives to be about 30 years old on average. And in that lifetime, it will have traveled 1.5 million miles, enough miles to have made three roundtrips to the moon. I’ve been lucky enough to see these birds at sea during fall migration. And every time I’ve seen one, I knew I was intercepting a miracle in progress.
But, it isn’t necessary to go out to sea to witness birds that undertake amazingly long-distance migrations. If you take a short drive to the coast, you can see the whimbrel. This is a shorebird that nests in Alaska and spends the winter along coasts from California to the tip of South America. They have been known to fly non-stop over the ocean for 75 hours and cover over 1850 miles in one stretch.
But, in reality, we don’t have to travel at all to witness a bird on a fantastic journey. We can just look out our window on a pleasant September morning. There, we are likely to see the very common, humble, and drab-colored Golden-crowned Sparrow. Or, we might hear it singing it’s mournful, descending “Oh dear me” song to itself. This bird has likely just finished a 2000 mile journey from southeastern Alaska. Point Blue Conservation Science (based in Petaluma) discovered the exact breeding grounds of our local Golden-crowned Sparrows by radio-tagging individuals.
How can the Golden-crowned Sparrow, a bird that weighs only a little over an ounce, travels such huge distances? First of all, it accumulates huge fat reserves by feeding constantly in the weeks and days before it leaves. But, it also needs plenty of food-rich rest stops along the way.
And then there is the problem of knowing when to take off and where to go. The urge to migrate is controlled by hormones. Birds navigate by sensing the earth’s magnetic fields and by orienting to the stars at night. The Golden-crowned Sparrow migrates at night. This sparrow only weighs about an ounce, and somewhere in its tiny brain, it has a sense of where stars should be at different times during the night and on different dates!?!
September is the month with the most bird movement.
As each day becomes shorter, our environment sounds, looks and feels different as new birds arrive and others slip away to places further south. These migratory birds are small but their feats are HUGE. These birds have senses that we don’t have. They can feel or see or sense magnetic fields that we are oblivious to. It makes you wonder how many different ways there are to perceive the world. Gosh, I guess there are as many different ways to perceive the world as there are individual organisms that have ever, or will ever live in it.
