Although they no longer worry about DDT, researchers today are concerned that the falcons may fall victim to other chemicals sprayed in the regions where the birds winter. High levels of the toxic industrial chemical PCB, for example, have been detected in three of every four peregrine falcons tested.
The satellite tracking system has already helped researchers determine where other birds may be encountering the toxic chemicals as they migrate, revealing the intimate ties between species in North and South America.
In a pioneering 1994 study, U.S. Forest Service ornithologist Brian Woodbridge, puzzled over an inexplicable decline in Swainson's hawks, used the satellite technology to track two hawks from the Butte Valley National Grasslands in northern California to the La Pampa province of Argentina.
It was the first time anyone learned where the endangered hawks spend their winter. When scientists subsequently visited the roosting spot, however, they discovered 700 dead hawks in nearby farmers' fields.
That was enough to trigger a more thorough investigation, and in 1995, researchers tracked 12 Swainson's hawks as they migrated from Saskatchewan, Idaho, Utah, California and Colorado. When researchers visited the nesting areas pinpointed by the satellite data, they discovered thousands of dead birds in the worst hawk kill ever recorded--all apparently poisoned by eating grasshoppers contaminated with the pesticide that Argentine farmers used for insect control.
The pesticide degrades so quickly that no residues were ever found in the blood or tissues of the hawks that survived to return to North America. Without the satellite tracking system, biologists might never have learned why so many thousands of hawks were vanishing.
The discovery led to a remarkably successful international rescue effort, and the birds appear to be recovering. Nonetheless, this fall, as the hawks begin their 12,400-mile round trip from California to South America, six more birds will carry satellite transmitters.
"The technology really saved that species," Seegar says.
Concerns Over Harming Birds
On the cliff face, Maechtle and Restani reset the falcon snare. They retreat up the rocks, as a gentle drizzle begins.
Seegar and Mattox train their scopes on the aerie and wait.
"Perched!" says Mattox. "She is caught."
Avoiding her slashing beak, Restani carefully lifts the falcon from the nest. Maechtle wraps a shawl around her wings then slides it into his fanny pack while he clambers up the cliff. Then Restani replaces the eggs in the nest.
Upon examination, they discover this falcon is no stranger. The information on its leg band shows it was first tagged in 1993, then caught again in 1995.
They loop the transmitter's Teflon straps around its wings, adjust the fit, and release the falcon.
The biologists acknowledge that their activities agitate the birds, but say that any harm they may do by capturing and tagging them is outweighed by the data they can gather, which may help ensure the survival of the species.
When the group first started tagging the Greenland falcons, the Danish government, which licenses the field research, was concerned the biologists might damage the hatchlings' chance of survival by handling the eggs.
But a controlled study of several hundred nests persuaded the researchers that they are not harming the birds or their young.
Indeed, several weeks after the falcon at Icecap Cliff was caught and released, four healthy fledglings hatched in the nest. The team bands all four--two males and two females.
In all, the team has mounted transmitters on six peregrine falcons in Greenland.
Now as summer turns into fall, the satellite signals indicate that the first of the peregrines has begun its annual flight south.
This month, Seegar hopes to catch a glimpse of the peregrines from his autumn bird-watching post at Assateague Island in Virginia, while Maechtle will be looking for them at Padre Island where they also often pause in their annual journey.
"They are on the move," Seegar says.
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Bird-Watching by Satellite
To better understand wildlife, researchers for some time have used radio transmitters to track animals. But conventional units are cumbersome and short-ranged, with signals easily blocked in mountainous terrain. New satellite micro-transmitters are so small that even bantam birds like the peregrines can fly with one strapped on their backs.
Satellites from a joint U.S. French service called Argos, moving in a low polar orbit, receive the signals
Transmitter size: 0.7 inches x 2.5 inches x 0.6 inches.
Weight: 1 ounce.
Power: 100 milliwatts.
Battery life: 1 year.
Transmission cycle: 8 hours a day throughout the fall mirgration season. Data is relayed every 4 days by electronic mail.
Cost: $4,000 for unit and one year of tracking.
Here are treks made by two of the falcons, one male and the other female, being studied.