How to Spy on an Albatross
With the help of tiny transmitters and orbiting satellites, scientists are discovering that birds have some astonishing destinations
There are stories--perhaps apocryphal, perhaps not--about ultrasecret spy satellites that can discern small details on Earth. They might, for example, count the albatross nests on Tern Island, an oddly shaped speck of land in the North Pacific Ocean, from 500 miles high. For the record, some 3,500 pairs of Laysan and black-footed albatrosses use Tern, part of the Hawaiian Islands National Wildlife Refuge, as a nursery. However, that number comes from a scientist´s informed estimate, not from an intelligence agency.
Still, the Tern Island albatrosses are being spied on from space. The satellites in question, however, are dedicated to monitoring Earth´s environment, not military and terrorist activities. And the information comes in the form of pulses of data from bird-based radio transmitters, not super-sharp pictures. For Tern is the site of an important study using satellite telemetry--a fast-evolving technology that has revolutionized conservation ornithology in a few short years--to track the travels of parent albatrosses as they fly far and wide in search of food for their earthbound offspring. Often those trips take them to dangerous waters.
In the process, Tern also has become a virtual science classroom for thousands of schoolchildren from Hawaii to Pennsylvania who are hands-on participants via the Internet in Wake Forest University´s Albatross Project, led by biologist Dave Anderson. Like the grown-up researchers at the North Carolina campus, the kids learn where "their" albatross went today by plotting coordinates relayed from Argos System satellites that scan for signals from the birds´ backpack transmitters on every pass.
One Laysan albatross, they determined, made four treks to the vicinity of Atka in the Aleutian Islands, a straight-line, round-trip distance of 4,000 miles--each time bringing home a liter of high-energy fish oil for its single chick. "That´s a long way to go for takeout," quips Anderson, adding, "We never imagined that a bird would fly that far north from Tern." At the same time, a black-footed albatross flew 24,840 miles in a three-month period on round-trips of as long as 28 days to foraging waters off the northern California coast.
Tern Island, lying 675 miles northwest of Honolulu, is an ideal base for Anderson´s study because of its accessibility to birds and biologists. From the air, it resembles an oversized aircraft carrier run aground on a treacherous atoll. The scenario is plausible: Tern is part of French Frigate Shoals, discovered in 1786 by a Gallic navigator whose two ships came within a tenth of a mile of smashing onto the reef, as an American whaler did 80 years later.
A reality check finds that Tern is little more than a 3,100-foot-long airstrip, built on the island out of crushed coral in the early months of World War II and serving much the same purpose as a flattop. The U.S. Navy´s Seabees also did a big favor for the albatrosses when they enlarged Tern. These slender-winged birds are indescribably graceful as they glide over the ocean waves for months on end, but they need a long and uncluttered runway for indescribably ungraceful takeoffs and landings during the time when they´re raising chicks.
Like similar projects involving other birds large enough to carry a platform transmitter terminal or PTT, as the device is known, the Tern Island study is partly about finding the answer to a question as old as human curiosity: Where do birds go when they leave their nesting places?
In the case of swallow-tailed kites that breed in Florida, their migration route and ultimate destination were unknown until 1996, when biologist Ken Meyer of the Avian Research and Conservation Institute in Gainesville first deployed PTTs on seven birds and tracked their 5,000-mile journey through Central America and onward to southeastern Brazil. American bitterns wearing transmitters on a bib instead of a backpack will tell John Toepfer, a biologist in Plover, Wisconsin, where this secretive marsh bird spends the winter.
Toepfer, whose work is partially funded by the U.S. Fish and Wildlife Service, uses a mirror and a tape recording of the bittern´s oong-ka-choonk vocalization to lure the territorial birds into a trap. "The bittern sees itself and attacks the mirror," Toepfer explains. "It works 7 out of 10 times." (Hanging the transmitter around the neck is necessary because a bird´s welfare is the first concern. Bitterns have a ridge on the back and a harness would roll and cause saddle sores.)
Guy Morrison, a biologist at Canada´s National Wildlife Research Centre in Hull, Quebec, hopes to "crack the abiding mystery" of where and why Hudsonian godwits pause on their fall flight from breeding areas around James Bay to wintering places along the coast of Patagonia and Tierra del Fuego. "There´s a gap of about six weeks between the time the birds leave Canada and when they arrive in Argentina," he says. "My guess is they stop somewhere in Amazonia. The rivers are lowest at that time of the year, and the godwits may be congregating on big sandbars."
But conservation concerns rather than scientific inquisitiveness are the main reason for the proliferation of satellite-tracking studies. A 50 percent drop in the western Arctic´s king eider population since 1976 prompted Lynne Dickson, another Canadian Wildlife Service biologist, to implant transmitters in 10 of these large sea ducks at nesting grounds on Victoria Island in the Northwest Territories. (Diving ducks won´t tolerate external transmitters.)
"We suspect the decline is due to changing conditions at molting and wintering sites, but we know very little about the location of these at-sea areas," says Dickson, who works out of Edmonton, Alberta. Her eiders traveled 2,100 miles to the Russian coast to molt their flight feathers, then recrossed the Bering Sea to wintering waters along the Alaska Peninsula and around Kodiak Island.
Another puzzle is why the eggs of white-faced ibis nesting at Carson Lake state wildlife area in Nevada are contaminated with DDT residue and show signs of being dented and crushed by the incubating adults. Eggshell thinning, which occurs when the metabolite DDE blocks calcium deposition during shell formation, once plagued bald eagles, peregrine falcons and brown pelicans. Now survival of ibis fledglings appears to be declining in the Great Basin--but the use of DDT in the United States was banned more than 25 years ago. "The problem has to be on the wintering grounds," says Charles Henny, a U.S. Geological Survey biologist who hopes to track the Carson Lake ibis to their unknown destination, possibly in Mexico.
"Finding out which areas are linked by a bird´s migration gives us a powerful argument for conserving those habitats," says Canadian Wildlife´s Guy Morrison. Researchers now know that swallow-tailed kites from the pasturelands of southwest Florida fly south to very similar savannah country bordering the Brazilian Pantanal--a vast wetland during the six-month tropical rainy season and rich grazing land for the rest of the year. "Kite habitat is threatened in both places by large-scale agricultural development," biologist Meyer says. "Saving private ranch land in Florida and Brazil has to be the focus of our planning effort."
Promising news is what Wake Forest University´s Anderson had in mind when he launched the Tern Island project. Albatrosses typically feed by sitting on the surface and seizing food items like squid and flying fish, which the birds then partially digest and mix with stomach oil to make a rich meal for their chicks. The birds are also habitual ship-followers. "They know good stuff comes off fishing boats," the scientist says. One of his transmitter-equipped black-footed albatrosses, Anderson relates, "was going nowhere in particular when it suddenly headed off on a straight-line track to San Francisco Bay. The bird broke off when the boat it was trailing went under the Golden Gate Bridge."
Unfortunately, thousands of albatrosses perish every year when they grab the baited hooks of longline fishing fleets. "I had hoped that our tracking data would pinpoint favorite feeding areas where the birds might be segregated from fishing activities," Anderson says. Preliminary results suggest that blackfoots head for the continental shelf between Santa Cruz, California, and Vancouver Island while Laysans wing to Gulf of Alaska waters between the Aleutians and the state´s southeastern panhandle. "These guys are covering such wide areas individually and collectively that we would have to close the entire northeast Pacific to fishing," Anderson laments.
None of these discoveries would have been possible in past years when ornithologists had to rely exclusively on conventional leg-banding with numbered aluminum rings to shed light on a bird´s travels. Only one of 117 bands put on swallow-tailed kites, for instance, was ever reported. The vast majority of recoveries come from game birds that are shot by the millions. Banding data from the wintering places of long-distance migrants, especially small songbirds like thrushes and warblers, are rare or nonexistent.
In May 1965, Bill Cochran, a University of Illinois electrical engineer, became a legend in the bird world after he assembled a tiny radio transmitter that weighed about as much as a dime and glued it to the back of a migrating gray-cheeked thrush. That night, the late Richard Graber, a biologist with the Illinois Natural History Survey, teamed up with the pilot of a Piper Cherokee sporting an array of antennas. They followed the thrush on a stormy, 400-mile night flight from Champaign-Urbana up the length of Lake Michigan to the tip of Wisconsin´s Door Peninsula. Nothing like this had been tried before.
Cochran is still tracking birds, using radio technology that was inconceivable 34 years ago and is still the only way to locate birds too small to wear satellite transmitters. "We can even hear the birds´ wing beats and flight calls," he says with some amazement. Following migrant birds by airplane is fairly routine today, but there are other problems beyond the relatively short range of the radio signals. In the mid-1980s, a time when prototype platform transmitter terminals for birds were first being tested, Granger Hunt of the Predatory Bird Research Group in Santa Cruz tried several times to chase radio-tagged juvenile bald eagles when they left their California birthplaces at the end of summer and flew north into Canada. He was thwarted either by bad weather or when he ran out of airports.
Hunt says, "I always figured the eagles were heading for the salmon runs in British Columbia or southeast Alaska where they could feed on carrion while learning to catch live fish." Recent data from the Argos-tracked flight of an eagle fledged at Lake Shasta suggests he was right. "We may learn from this study that the ecology of California bald eagles is tied to the health of the northern salmon run and thus to the abundance of plankton in the Pacific Ocean," he adds.
Cochran, meanwhile, remembers that in the early 1960s he and a colleague asked the National Science Foundation to fund satellite tracking of wandering albatrosses, the largest flying bird. "We weren´t taken seriously," he says. "Our idea was comic relief after a long day of reviewing proposals from other researchers." Not until the mid-1970s, when biologists Frank and John Craighead put a 10-pound, shoebox-size transmitter on a Yellowstone National Park grizzly bear, was a wild animal tracked by satellite. A two-pound transmitter was available by the end of the decade and was widely used on large mammals, but it was far too heavy to be carried by a migrating bird.
The breakthrough came when Bill Seegar, a biologist at the U.S. Army´s Edgewood Research and Development Center on Maryland´s Eastern Shore, and Paul Howey, a waterfowl specialist who was intrigued with electronics, resolved to find a way to track endangered peregrine falcons from northern breeding cliffs to their winter destinations. They asked engineers at Johns Hopkins University´s Applied Physics Laboratory to build a battery-powered satellite transmitter small enough to be carried by a peregrine. The prototype, weighing about six ounces, was tested on a mute swan in Chesapeake Bay during the summer of 1983, and first-generation platform transmitter terminals were soon being used to follow the migrations of eagles and other large birds.
But Seegar had to wait another 10 years before there was a satellite transmitter small enough to be strapped to a falcon´s back. The challenge was to design microelectronics to control the transmitter while keeping power consumption to a minimum. Howey had started his own company, Microwave Telemetry in Columbia, Maryland, to design and produce satellite transmitters for wildlife research. In 1993 he delivered a one-ounce unit that female peregrines, which are larger than the males, could safely carry.
Seegar and his colleagues have since mapped peregrine migratory paths from Alaska, the Canadian Arctic and the Greenland ice cap to points as far south as the wind-swept altiplano (high plain) of Argentina. The researchers had assumed that peregrines would winter in coastal areas, but one falcon homed in on a 10-acre marshy oasis in the middle of a barren Andean salar (a salt desert) 13,000 feet above sea level where sandpipers, a favorite prey, were abundant.
Howey´s smallest platform transmitter terminal now weighs less than seven-tenths of an ounce. The hermetically sealed housing is about the size of a BIC lighter with an eight-inch stainless steel antenna. Inside is an electronic module with sensors to measure temperature and an animal´s activity. The unit can be programmed to transmit at a steady rate during migration and be virtually dormant when the bird is nesting and sedentary. The cost is $2,800--not including satellite time.
Will satellite transmitters get much smaller? Howey doubts it will happen unless there is another breakthrough in the design of batteries that account for most of the weight. A minuscule device that might be carried on migration by a one-ounce gray-cheeked thrush appears to be a pipe dream.
Yet John James Audubon, who in 1803 tied silver cords to the legs of nestling phoebes and identified two of them when they returned as adults to his Philadelphia neighborhood the next year, never would have dreamed that in 200 years it would be possible to spy on birds from space.
Field editor Les Line is a former bird-bander who studied the winter wanderings of evening grosbeaks, purple finches, tree sparrows and blue jays. Wake Forest University´s Albatross Project can be found on the web at www.wfu.edu/albatross .
How Satellites Track Birds
French-American Argos satellites, dedicated to monitoring Earth´s environment, collect data on every orbit from several hundred platform terminal transmitters (PTTs) attached to birds ranging in size from condors to ducks. Typically, a PTT transmits for less than one second every minute, sending an identification code along with such information from on-board sensors as a bird´s flight altitude. Ground-based computers use the Doppler effect--shifts in the frequency of the received signal due to the satellite´s motion--to calculate the location of a bird to within six-tenths of a mile.
In the near future a new generation of PTTs may carry not only a more accurate Global Positioning System receiver but also a sensor that can recognize behavioral calls and even a tiny camera to send back pictures of a bird´s habitat and nest.