Migration brings back boyhood memories
Last October, under bright moonlight conditions, I heard two separate flocks of Sandhill Cranes migrating south, sounding their “gru gru gru” reminding me of my boyhood and my dog.
Fifty years ago my family camped on our property on Harmony Ridge, just east of Nevada City. A pre-teen, I was sitting on a rock outcrop next to my springer-cocker spaniel with a crystal clear view of Banner Mountain. My dog suddenly became tense, her muscles stiffening. A deer? No, she was looking very intently high in the south-eastern sky. Five minutes later I heard what she was silently pointing out. The exciting guttural call of a migrating flock of Sandhill Cranes came to me. They became louder. Still, I could not see them. Guided by her tracking gaze, at last I saw the group of 20 cranes. But, then, they seemed to disappear. They were circling in a thermal gaining altitude.
Sandhill Cranes migrate along the pacific flyway heading to their wintering grounds in central California from their summer breeding areas. The birds flying over Nevada City begin their migration as far north as the Bristol Bay lowlands on the Alaska Peninsula or as near as the Malheur wilderness in Oregon. Adult cranes were captured, equipped with transmitters, and tracked by satellite to determine their migration routes and wintering areas. Some hardy individuals of the lesser sandhill subspecies were discovered traveling all the way to Siberia to breed.
Fossils more than 6 million years old found in Nebraska make the Sandhill Crane the oldest still-living species of bird. Nebraska is still a major staging area for cranes as up to 550,000 gather each year along the Platte River.
Hunting may affect some populations, such as the Rocky Mountain flock whose population may be slowly declining. Sandhill Cranes are hunted for game in 12 western states, two Canadian provinces, nine Mexican states, and portions of Russia. Hunters take more than 25,000 birds each year. Cranes are harvested conservatively because these long-lived birds have a naturally low reproductive rate.
Why are they so difficult to locate and keep track of in the sky? Cranes continually emit their cries in flight. When they circle and face away from you, the listener, their calls fade into nothingness. Then, as they continue to wheel around toward you, the sound comes directly at you. The calls cycle from loud to very soft, over and over, as round and round they go riding a thermal air elevator.
When the cranes emit calls face-on, they present a slim profile, which is difficult to see. While this sound is racing to you at 1,100 feet per second, the birds continue to circle, now presenting the broad profile of their wide wings. But, as you try to sight the birds from the travel-delayed sound, again they have assumed the slim, face-on view which is hard to see. Now, of course, another burst of calls is on its way to you. Say, if they’re a mile away this new sound will reach your ears in five seconds after they’ve completed another whirl to the face-on view. If the cranes are more than a mile away, the complexity of sighting the birds increases. Because of this sound delay phenomenon locating a flock can be frustrating, especially through tree branches.
Now retired, and with a new companion dog, I look forward to the yearly north-south, (October) and south-north (March) migrations of the sandhills over my home near that rock outcrop and the old campsite. The cranes, my companion dogs, and me form a lasting and a continuing memory of the Sierra foothills.
Walt Carnahan is president of the Sierra Foothills Audubon Society.
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