Donna
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« on: 13-Oct-09, 09:52:12 AM » |
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Scientists and volunteers prepare a net to capture red knots on the Mustang Island beach. The Texas coast is a stopping point on the birds' long migrations and a possible wintering ground for birds not old enough to make the entire flight.
MUSTANG ISLAND — The cannons were loaded. The trigger woman was crouching behind a Jeep. The net was in position.
The volunteers were told to start “twinkling,” a herding maneuver designed to move birds up the beach.
“They may call it twinkling,” David Newstead, an environmental scientist at the Coastal Bend Bays and Estuary Program in Corpus Christi, said of his British and East Coast colleagues. “But we call it the Texas red knot roundup.”
Red knots are robin-sized birds with 20-inch wingspans. For the past week, ornithologists from England and New Jersey have worked with local scientists, wildlife managers and birders to trap and tag 200 of them on the Texas coast.
Each year, red knots fly from the Canadian Arctic to the southern tip of South America. The 20,000-mile round trip is one of the longest and least understood migrations in the animal kingdom.
The Texas coast is one of the known stopover points and possible wintering grounds for immature birds not old enough to make the entire two-continent flight.
Red knots have been intensely studied on the East Coast, but little is known about where the birds that stop in Texas are coming from, how long they stay and where they go.
Thus the tagging. But to do that, the delicate birds have to be captured.
That's where the three cannons come in.
First, the team digs a shallow foot-wide trench in the beach about 20 yards from the water's edge. They place a folded 23-by-12-yard net inside. The end of the net is attached to three weights; each is loaded into a cannon facing the water. A car sound system attached to a battery is then buried nearby; it plays the red knots' roosting call, which sounds like hundreds of kids squeaking their shoes on a basketball court.
Everything is hidden under a thin layer of sand and scattered seaweed.
The team then breaks into groups, one to keep the public away, one to trigger the artillery and the other to try and “twinkle” the birds toward the net.
“It's about the least manly thing you can herd,” said Rafael Calderon, a biology graduate student at Texas A&M University-Corpus Christi, who was using his pickup to do it.
To get the birds into the “capture zone,” Calderon and Newstead slowly drove their trucks, sometimes into the water, getting as close as they could without scaring the birds into flight. Newstead got stuck once and had to be towed out. Eight birds made their way toward the net.
Habitat loss and overharvesting of horseshoe crabs, one of the bird's favorite midmigration foods on the East Coast, has driven the known populations of red knots down as much as 80 percent in the past 15 years, said Larry Niles, who is leading the research of the bird in the Americas under federal and private grants.
Red knots also migrate from the northern reaches of Asia and Europe to the southern tips of Africa, Australia and New Zealand. Because the birds depend on the ecosystems of two continents, any change in their behavior and populations can offer insight into what is happening, not only for other shorebirds but also larger changes, such as global warming, Niles said.
“Shorebirds become an indicator for where we are headed with that,” he said.
Finally, the birds were in place. The countdown came over handheld radios, and with a “bam!” and a cloud of sand, the net flew over the birds.
Team members ran to gather the birds and put them into padded plastic totes. Sitting in a circle, they weighed them, took measurements and feather samples, placed the tags and then set the birds free.
Each bird scrambled back to the water's edge. Kicking its legs several times, each one got used to the bright plastic around its leg, then got back to looking for clams.
They had a long flight ahead of them.
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