Tracking by satellite solves bird migration riddles

Tracking by satellite solves bird migration riddles

By Rex Graham

Bryan Watts has witnessed the death of other birds, but he was particularly disheartened about a Whimbrel flying toward what he assumed would be its certain death. Tracking by satellite, Watts was trying to solve a bird migration riddle when a ferocious storm turned his experiment into a nightmare.

The ornithologist had captured the Whimbrel with its characteristically long, downward-curving bill in the Arctic at the northern tip of Canada’s Northwest Territories. Watts attached a tiny $4,000 solar-powered satellite-tracking device to reveal how, when and where the bird migrates.


The Whimbrel, a shorebird about the size of a pigeon, is one of about 2,000 bird species worldwide that migrates. Photo: Aaron Maizlish)

This new generation of lightweight, solar-powered satellite tracking devices is revolutionizing ornithology, giving scientists like Watts surprising insights about the migration of the Whimbrel, White Stork, Eleonora’s Falcon, Wandering Albatross, Snow Goose, Steppe Eagle and many other birds. This fall as birders watch flocks fly south, tracking data is flowing into databases around the globe.

The Whimbrel, a shorebird about the size of a pigeon with longer legs and bill, is one of about 2,000 bird species worldwide that migrates. Metal bands attached to the ankles of millions of migratory birds have been the mainstay of ornithology for more than a century, but bird banding has not solved many bird migration riddles.

Bird migration riddles

Ornithologists like Watts want to know precise starting times, routes, flying speeds, stopover locations, fatality circumstances, wintering and breeding destinations, and many other details about one of the most extreme behaviors in the animal kingdom.

Bryan Watts,

“One of the most important kinds of results this technology is providing is what we call ‘connectivity’ between a species’ breeding and wintering areas,” said Bryan Watts, a biology professor at the College of William and Mary in Williamsburg, Virginia, and director of its Center for Conservation Biology. (Photo: College of William and Mary)

“It’s a completely new ball game now,” said Watts, a biology professor at the College of William and Mary in Williamsburg, Virginia, and director of its Center for Conservation Biology. “One of the most important kinds of results this technology is providing is what we call ‘connectivity’ between a species’ breeding and wintering areas.

How birds die

“There are many questions we could never answer before, and the new information that these technologies are providing is priceless,” he said. “We can know if they die, where they die and when.”

In 2011, two other Whimbrels with satellite trackers – Machi and Goshen – negotiated Hurricane Irene on their fall migration, but were shot by hunters a few days later on the Caribbean island of Guadeloupe. An international outcry led to the adoption of a no-hunt list of species and a bag limit of 20 birds per day for other shorebirds that routinely use Caribbean “shooting swamps.”

The more dangerous migratory path of a Whimbrel named “Hope” was on his mind in August 2012, while attending an annual meeting of the Western Hemisphere Shorebird Group in Vancouver, British Columbia. Many of Watts’ colleagues at the meeting would soon be caught up in the life-or-death drama of Hope.

Whimbrel collision course

Hope’s data points moved 55 miles per hour from the Mackenzie River on Canada’s north coast on the Beaufort Sea, southeast across Canada directly toward Tropical Storm Gert churning the North Atlantic Ocean.

In this case, the data points were generated by a satellite-tracking device made by Columbia, Maryland-based Microwave Telemetry, Inc. Beginning in about 2006, companies like Microwave Telemetry began making tracking devices for wildlife research. The Global Positioning System (GPS) of earth-orbiting satellites is an integral component of 21st century tracking of birds.

The first generation of trackers were large and bulky, but worked well for Badgers, Bighorn Sheep and Grizzly Bears, but they were too heavy for birds. However, over the next few years, several companies miniaturized the technology. Some weight as little as 4 grams and include tiny solar panels that charge a light-weight battery.

Tracking birds by satellite

Ornithologists who have used satellite tracking use words like “remarkable” and “striking” in their otherwise dry prose in scientific papers. Some use less expensive, less sophisticated geo-locators. They weigh less than 1.5 g and cost only about $100.

These sensors have an internal clock and light sensor. Measurements of sunrises and sunsets yield the time and location of the tagged bird to an accuracy of roughly 50 kilometers.

However, the loggers must be retrieved to download the data. They work well for birds that return to the same burrow or patch of forest to breed every year.

Kestrels, latitude and locusts

Lesser Kestrels,

Lesser Kestrels migrating south from Spain in the fall cross the Mediterranean on a broad front to “a small latitude belt” where locusts are plentiful. It’s migration routes and behaviors have been bird migration riddles. (Photo: unknown, public domain)

When both geolocators and satellite trackers were used on the same species, the Lesser Kestrel, the verdict of ornithologists was unequivocal: [wlm_private_Subscriber annual]“Geo-locators do not provide adequate data to estimate migration parameters in detail, e.g. flight speed, time budget or individual variation of routes,” said Ruben Limiñana, an ornithologist at University of Alicante in Spain.

Limiñana and his colleagues used 5-gram solar-powered satellite-tracking devices made by Microwave Technologies.

They learned that Lesser Kestrels migrating in the fall from Spain crossed the Mediterranean Sea on a broad front to “a small latitude belt” running through Senegal, along which locusts and grasshoppers, their favorite prey, are plentiful. In the spring the kestrels returned to their breeding grounds in Spain via the Strait of Gibraltar, using a clockwise loop that skirted areas with frequent sandstorms.

Steppe Eagle surprises

Steppe Eagle,

Steppe Eagle nest, Lower Volga River, Russia, June 2010. (Photo: Peter Wernicke)

Steppe Eagles have been declining, and nobody knows why. They breed in the vast, sometimes treeless steppes of southeast Russia to eastern China, and winter in Africa as far south as South Africa. They can spend three months a year migrating.

Satellite tracking revealed that Steppe Eagles use a clockwise migratory loop around the Red Sea to and from Africa. A group led by Bernd-Ulrich Meyburg, a distinguished raptor expert and chairman of the World Working Group on Birds of Prey, attached satellite tracking devices to 16 eagles in a tracking study to find that most winter in Tanzania.

However, Meyburg’s group was surprised to discover that many eagles winter on the Arabian Peninsula, where herds of domestic goats, sheep, cows and camels have increased dramatically.

Steppe Eagles systematically seek animal carcases that have been left lying. “It is now not unusual to see 50-100 birds together,” Meyburg’s group wrote in a 2012 report in British Birds. He speculates that the new food supply may be fundamentally altering the species’ migration.

Falcon insect hunter

Eleonora’s Falcon,

Eleonora’s Falcons breeds on islands in the Mediterranean, winters in Madagascar and southern Africa, and hunts insects at “staging areas” 400 km inland from their island breeding colonies. (Photo: Ugo Mellone)

Eleonora’s Falcons breed on islands in the Mediterranean and winter in Madagascar, and telemetry studies have shown that these long-distance migrators use inland Africa instead of the coast. Even during pre-breeding, all three falcons with tracking devices move inland 400 km from island-breeding colonies to “staging areas” from forests to farms to hunt insects. The birds repeated the pattern annually in a four-year study.

“We suggest that conservation measures implemented at breeding and wintering grounds may not suffice, and that temporary staging areas should be identified at a large scale and deserve protection as well,” wrote Ugo Mellone in a 2012 paper in Bird Conservation International.

California Condor roaming

The most-tracked bird species is the world is the California Condor, but it doesn’t migrate. Even before its numbers in the wild plummeted, field biologists often didn’t see any condors for weeks. Its numbers have increased thanks to a captive breeding program.

California Condor roosting areas,

California Condor roost-site-density map in southern California created with satellite telemetry data, 2005-2012; red is high density of roosts, dark blue is low. (Graphic: Christopher Cogan, U.S. Fish and Wildlife Service)

With 237 condors living in the wild (198 are in captivity), as of May 31, 2013, wildlife biologists want to know where the birds are nesting, hunting, perching and roosting. “In the old days it was all visual,” said Christopher Cogan, a professor of environmental science at California State University, Channel Islands, and co-author of an analysis of condor satellite tracking data. “Sending out field teams was a huge expense and we wouldn’t see them for days or weeks even then. Satellite tracking is a game changer.”

Using electronic tracking technologies over seven years, 340,694 positions from 51 total condors was recorded by time and place. Suddenly, a detailed picture of condors began to emerge from all the data. Breeding pairs of condors were tagged, however Cogan and his colleagues at the U.S. Fish and Wildlife Service would lose individual bird’s signals each time one flew into cave-like nesting sites to brood eggs or tend to chicks.

California Condor,

California Condor #98 is one of dozens of condors in southern California outfitted with solar-powered satellite tracking devices. (Photo: Angela Woodside, U.S. Fish and Wildlife Service)

“We used the loss of signal to say that bird is on the nest, and we could see male-female exchanges,” Cogan said in a telephone interview. “If both birds left the nest site and it was too early for fledging, we could say that nest had failed.”

In some cases, Cogan said that California Condors that were born and raised at places like the San Diego Zoo Safari Park and released in Southern California ended up in the same canyons where ornithologists had removed condor eggs from nests in the 1940s. “There are some amazing similarities we discovered by comparing historical records with satellite telemetry data,” Cogan said.

River runs through it

Bonellis Eagle breeding territories,

Breeding ranges of two Bonelli’s Eagles: “M1’s” tracking by satellite measurements are represented as gray triangles; “M2’s” breeding territory is represented as black dots. (Image: Juan Manuel Pérez-García, Journal of Ornithology)

A satellite telementry study published in 2012 showed that Bonelli’s Eagles in Spain have breeding territories that don’t overlap. It showed that two pairs of eagles shared a river boundary for their respective home ranges, each about 200 square km. However, occasionally a Bonelli’s Eagle will travel long distances out of its home range, possibly looking for better territory with more prey, or even sizing up reproductive options. Females ventured more than three times farther than their male partners.

Hope bird struggles

Whimbrels add 50 percent in body weight before migrating, and routinely fly 4,400 miles non-stop for six days. When they come down, they don’t forage very far, instead targeting a particular shoreline loaded with fiddler crabs. They sometimes gorge on blueberries at commercial acreages in Maine or Nova Scotia.

“They go to places with super-abundances of food, often to the same creek every spring,” Watts said. The migratory paths of Whimbrels, like that of many other long-distance migrants, had been pieced together over the from binocular observations and banding studies.

The first Whimbrel fitted by Watts with a satellite tracker in 2008 flew 5,057 km from Virginia to the MacKenzie River delta without refueling in six days flat. It flew non-stop at 35 km per hour, Watts said.

In 2012, Hope was flying faster, taking advantage of prevailing winds with other Whimbrels, probably in a V-formation. They headed east across Canada and then south over the Atlantic toward St. Croix, one of the U.S. Virgin Islands. But Hope encountered Tropical Storm Gert. When Hope’s speed dropped into the single digits for hours, Watts assumed it couldn’t survive.

But the bird’s satellite tracker kept reporting, as Hope battled Gert’s wind. “It was in the storm for 27 hours,” Watts said. Then Hope emerged.

Migratory ‘situational awareness’

The bird took an unexpected right turn, taking advantage of suddenly shifting winds and soon landed in Cape Cod.

“It’s one of the many things about these birds that surprised me,” Watts said. “They have incredible situational awareness.” Hope and its fellow Whimbrels remained in Cape Cod for a few days, recovering, then took a 1,000 km hop to Virginia for fiddler crabs. Refueled, the birds continued south to St. Croix.

Watts says southward migrating Whimbrels seem to avoid the western Atlantic near the U.S. East Coast because the chances of hitting a storm there are higher than over the mid-Atlantic’s colder waters. He followed Hope for four years, while it flew a total of 100,000 km (60,000 miles).

Hope’s antenna final broke off, so Watts couldn’t track her on her 2013 migration, but her colored-plastic leg band remained. “We never understood how Whimbrels negotiate Hurricane Alley,” Watts said. “It was a question we couldn’t answer until now.”

Million-mile migrator

Whimbrel "Hope"

Lisa Yntema, a St. Croix ecologist who collaborates with the Center for Conservation Biology, holds “Hope” after the Whimbrel successfully migrated directly through Tropical Storm Gert. (Photo: Fletcher Smith, Center for Conservation Biology)

The story of Hope continued in 2013, even without its tracking device. “A lady in St. Croix reported seeing her this fall, in St. Croix’s Great Pond, a mangrove patch,” Watts said.

The Arctic Tern is considered the champion long-distance avian migrator, migrating from the Arctic to Antarctic and back again once a year. The round-trip distance can be more than 70,000 km (43,500 miles) each year. They live 30 or more years.

Terns easily fly a million miles and rest when tired, floating on water like a duck. They can refuel in the open ocean. Whimbrels and other shorebirds such as Bar-tailed Godwits and Hudsonian Godwits add 50 percent in body weight and fly non-stop thousands of kilometers non-stop.

“They’re all pretty spectacular,” Watts said.

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