PALMER, Alaska (AP) -- You could hear the sandhill cranes coming.
Wave upon wave of calls chittered across the valley with tremendous urgency, getting louder with each second. As the sound filled the sky over a Matanuska Valley farm, biologist Mike Petrula sat up in his hiding spot under a spruce tree and scanned the field with binoculars for landing cranes.
''It sounds almost prehistoric,'' he muttered.
Thousands of these cranes arrive through upper Cook Inlet during the spring migration from California to Alaska. Some nest here for summer, others move west to Bristol Bay and beyond. And in the fall they return south in high, jabbering flights. But many details -- where they go, where they eat -- remain unknown.
To find out more, Petrula and other biologists from the Statewide Waterfowl Program in the Alaska Department of Fish and Game plan to capture a dozen birds this season and then track them with satellite transmitters during the coming year. A week ago, the scientists came to a potato field near Trunk Road to draft the first three volunteers.
After an hour of waiting, no cranes had approached the cracked corn spread on the ground to lure adult birds within reach of a rocket-propelled seine net. Now that was about to change.
The noisy flock suddenly appeared above the trees, silhouetted against the snowy skyline of Pioneer and Twin peaks. Their high-pitched racket was otherworldly, more like a discordant jumble of human voices than bird calls. The cranes circled in unison then cupped their broad wings and crooked their long necks forward and descended into the field. More cranes followed them in. Within minutes, a few hundred birds milled among shriveled potatoes and old stalks.
For a time the cranes -- 3 feet tall, with long black legs, red foreheads and gray plumage -- flirted with the bait, pecking the ground and bickering among themselves. One would spread its wings, jut out its neck and lunge at another, which would pop up or dash away. At one point, a bird even straddled the folded net. A half dozen birds finally gathered over the corn, only to stride from the target zone en masse, as though obeying some avian command.
A few minutes later, a row regrouped and slowly walked back into the corn. Petrula radioed his co-workers hiding in brush at the edge of the field to detonate the rockets.
The rockets boomed, yanking up the 60-foot by 30-foot net. As Petrula and five other biologists dashed forward, hundreds of cranes exploded into the air, calling and crying and squawking.
Nine cranes were trapped.
One large adult fought toward the edge, unbowed and seemingly unafraid. With furious yellow eyes, the crane hissed at the approaching humans, lunging with its open black bill.
More than half a million cranes return to the North each April and May, nesting in marshes and wet tundra from northern Canada through Siberia. Most of Alaska's cranes summer in the Yukon-Kuskokwim Delta, the Yukon Flats and the Tanana River Valley as well as Canada and Siberia.
But a small, apparently distinct group summers in upper Cook Inlet, Kenai Peninsula, Alaska Peninsula and Bristol Bay. This lesser-known bunch follows the Pacific Flyway -- the Copper River Delta, Southeast Alaska, British Columbia, Washington, Oregon -- to wintering grounds in California's central valley.
The Pacific Flyway population has been estimated at up to 25,000 birds, but there's been no reliable count and much about these local cranes remains unknown. Do Bristol Bay cranes travel their own course through British Columbia? Do these cranes always go to the same wintering sites? Are there variations in size, genetics, habits?
Last July biologists with the Department of Fish and Game obtained six satellite transmitters, with funding from the U.S. Fish and Wildlife Service. Petrula and others with the waterfowl program captured four young cranes at the Palmer Hay Flats and two from the Anchorage coast.
Three of them died that summer in Alaska: One was legally shot by a hunter near Hope and two were killed by predators. Of the three cranes that flew to the Lower 48, one died in December in central Oregon. But two cranes, both from the Palmer Hay Flats, made the full round trip, giving biologists unprecedented detail about their migration.
After wintering in Galt, Calif., a female crane began moving north in March. Between April 18 and April 28, the bird traveled from central Oregon to the coastal refuge outside Anchorage. The other bird, a male, wintered near Lodi, Calif., and had made it to Lituya Bay southeast of Yakutat by April 28.
''It worked out pretty good,'' said Petrula, who kept the Web site updated throughout the winter. ''This season, we want to increase our sample size.''
The biologists plan to clamp satellite transmitters to the legs of 12 more birds -- three adults in April and nine birds-of-the-year in July, Petrula said.
But first they have to capture them.
In the Matanuska potato field, six state biologists scattered to individual cranes pinned by the net. The men lifted the mesh, untangling talons and beaks and wings, then guided the birds out so they could be wrapped up for measurements or freed.
In a few minutes, the biologists had released three of the smaller birds -- they dashed across the field and leaped aloft. The rest were wrapped in bags and hoods, legs secured with Velcro straps, or held by biologists. The bird cradled by Dan Rosenberg held its head up, glaring with yellow eyes. It pulled at his shirt with a talon, then shot its bill toward his face. Finally Rosenberg let it clamp down on his gloved thumb, which seemed to calm the bird.
In turn, a pair of biologists would squat and quickly measure bill length, leg bone, the middle toe and nail, and a portion of the wing. Alaska's biggest game birds, these cranes weighed 8 1/2 to 9 pounds -- their black flexible bills extending 4 inches, middle toes reaching more than 3 inches to end in sharp black nails. Blood was taken from the under the wing to find out sex and genetic heritage. Biologists clamped leg bands on four birds, so they could be identified if sighted, captured or shot in the future.
And three birds each received a 1-ounce satellite transmitter -- a small yellow cylinder placed around a leg. For the next year, the $3,000 units will send out a pulse every 60 seconds, giving fixes to one of four polar satellites. Their progress across Alaska and North America will be posted on the Web.
Details on their migration can be found at: www.state.ak.us/adfg/wildlife/duck/crane/crane.htm.
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