E6

Science

URBAN JUNGLE

The changing natural world at our doorsteps.

Preflight fueling

In early spring, blowflies emerge from the ground’s top two inches of soil, where last fall’s late-season maggots overwintered.

Bigger than a housefly, these “bottle flies” are often seen basking on sunny outdoor walls. A fly will sponge up flower nectar, such as from the spicebush blossoms shown below, but if its antennae catch the scent of decaying flesh — as far as 10 miles away — the insect will launch a relentless search for it.

KLMNO

Rare bird’s numbers take a sudden dive

cranes continued from E1

cousins. By one estimate there were fewer than a thousand in the world in the early 1800s. (About 650,000 sandhill cranes come up the Central Flyway to- day.) Their nesting ground, in a Canadian national park strad- dling the border of Alberta and the Northwest Territories, wasn’t discovered until 1957. What is certain is that the whooping crane nearly went ex- tinct in the first half of the 20th century, its population bottom- ing out at 14 or 15 individuals in the spring of 1941. Since then, like an individual whooper tak- ing flight, it’s been a long, slow upward climb. As a consequence, the deaths

Female blowflies will lay eggs on dung or rotting vegetation, but fresh carrion is their preferred breeding site. The tiny eggs are deposited in “rice ball” clumps of 200 that quickly hatch into maggots, which grow, molt, pupate and emerge as adults within two or three weeks.

Blowfly maggots are so effective at devouring necrotic tissue that they are sometimes used by surgeons to clean out wounds and stimulate healing. Used for

centuries, maggot therapy has

been readopted by numerous wound-treatment centers after the practice fell out of favor in the mid-1940s.

SOURCE: University of California at Riverside; University of California at Irvine

PATTERSON CLARK/THE WASHINGTON POST

of even a few whooping cranes get the attention of researchers such as the ones here at the 30- year-old Platte River Whooping Crane Maintenance Trust. This year for the first time, the move- ments of a few birds are being monitored in real time through miniaturized leg-band Global Positioning System devices. This research project took six years of meeting, discussing and permit-getting in two countries. It is finally underway, at a propi- tious time. A census of whooping cranes conducted last spring as the birds were preparing to head north revealed a startling spike in mortality. Fifty-seven had dis- appeared in the preceding 12 months. Twenty-three of them died on the wintering grounds at the Aransas National Wildlife Refuge, on the Gulf of Mexico about 50 miles northeast of Cor- pus Christi, Tex. The rest appar- ently died during migration. (A smaller population of cap- tive-bred and released whooping cranes in Florida has had differ- ent problems. Although some of the birds have been successfully taught to migrate to a breeding site in Wisconsin, almost none produced offspring.)

Every six hours

Wintertime mortality is usu- ally very low in the Texas-to- Alberta wild flock, often only

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Whooping crane highway

Whooping cranes migrate every year from Texas to Canada along a path called the Central Flyway. During this spring's migration, researchers are getting pinpoint data from two cranes carrying GPS tags in hopes of better understanding the rare birds’ habits.

ANNUAL CIRCUIT

May-September

Birds breed in Wood Buffalo National Park in northern Canada

October-November

Fall migration south

November-March

Winter at Aransas National Wildlife Refuge on the Texas Gulf coastline

March-late April

Spring migration north

U.S.

Most whooping cranes stop here

every year to rest and feed, most for a day

or two but some for as much as two weeks.

SOURCES: Platte River Whooping Crane Maintenance Trust; U.S. Fish and Wildlife Service.

GENE THORP AND BONNIE BERKOWITZ/ THE WASHINGTON POST

MEXICO

March 19

Aransas Nat’l Wildlife Refuge

Gulf of Mexico

March 28

CANADA

March 28

Wood Buffalo Nat’l Park

Selected GPS locations

Juvenile, probably a male, traveling with two other cranes.

Female half of a crane couple traveling together.

one or two birds. While the reason for the large number of deaths two winters ago isn’t known, some may have succumbed from a shortage of food. The Aransas wetlands were notably dry that year, reducing the number of blue crabs, a major constituent of the whooping crane diet. While sandhill cranes happily feast on waste grain in the muddy crop fields of the Platte River ba- sin, whooping cranes greatly pre- fer animal to plant material. They eat snakes, lizards, clams and dragonflies (but rarely fish, which they seem to have a hard time catching). Although great bird artist John James Audubon be- lieved incorrectly that whooping cranes and sandhill cranes were the same species, with the sand- hill’s gray-brown a juvenile col- oring, his portrait of the whooper was dead-on. He depicted the huge bird preparing to devour two just-hatched alligators. “Species that are very specific in their diet are much more vul- nerable. That seems to be the case with whooping cranes,” said Ka- rine Gil, a population ecologist at the Crane Trust. What caused the deaths of the

LM OTERO/ASSOCIATED PRESS

Two whooping cranes take to the air at the Aransas National Wildlife Refuge in Texas.

migrating birds isn’t known, ei- ther, although the conventional wisdom attributes most fatalities to collisions with power lines. Nine whooping crane carcasses recovered in recent decades sug- gested such a death. But Felipe Chavez-Ramirez, the biologist who heads the Crane Trust’s research station, doubts that’s the whole answer. “We think that under normal flying conditions the cranes should be able to get around them,” he said this month. He, Gil and their collaborators,

however, may be about to get a more complete picture of the haz- ards of migration, and of the suc- cessful features of it as well. They have permission to trap and band 10 whooping cranes in the winter and 10 in the summer for three years. It’s a big job, and potentially dangerous for all con- cerned. Trapped birds can devel- op a potentially fatal muscle ail- ment called capture myopathy. Bird-banders can get pecked or scratched. The birds are caught with a rope snare that lies on the ground and is attached to a bent fishing rod. When a walking crane trips it, the rod recoils and tightens the leg noose in a way designed not to traumatize the bird. Two whoop- ers were outfitted with GPS an- klets last winter. Start to finish, the procedure took 15 minutes for one and 16 minutes for the other.

TUESDAY, MARCH 30, 2010

Each device costs $4,500, and

the tracking service, provided by a private company, costs $1,500 a year. The anklets are solar-pow- ered and designed to last at least three years. In a trial run the re- searchers last spring put devices on two sandhill cranes; they’re still working.

With a weight of less than three ounces — a little more than 1 percent of an adult crane’s weight — the tracking device isn’t expected to hamper a bird’s flight. Every six hours it records its position and uploads the in- formation to a satellite. If a crane’s location doesn’t change for 24 hours, the scientists mon- itoring the data stream will con- clude something has happened and go looking for the bird. More than 90 percent of the scheduled transmissions from the two whooping cranes have come through. Late last week the birds were in Kansas, not Ne- braska; near each other, but ap- parently not traveling together, Gil said. What kills whooping cranes is only the crudest of facts the sci- entists hope to get out of the project. “We hope to learn something about their habitat-use pat- terns,” Chavez-Ramirez said. “Where do they spend the night? What are the characteristics of those sites, the depth of the wa- ter, the vegetation? We’ve never had a quantifiable way to evalu- ate where they roost.” Wetlands are being lost throughout the birds’ migration route, he said. The tracking pro- gram “will let us understand what they want and what they use so that perhaps we can re- produce those conditions.” It may also help answer more

speculative questions. As part of her research, Gil has

correlated climatic variables with the whooping crane popu- lation size and the reproductive success of birds identified by col- ored leg bands (including one four-generation lineage). She has found that the population declines in rough synchrony with the Pacific Decadal Oscilla- tion, a pattern of Pacific climate variability similar to El Niño. This decline is probably due to weather extremes during those years: low temperatures, which stress the birds, and a shortage of rain, which lowers water lev- els and exposes their nests to predation. A better picture of where the birds are, and how they die, will help test her hypothesis.

browndm@washpost.com

Ancestors of T. rex lived in Australia

Bone discovery is first to place dinosaur in Southern Hemisphere

by Amina Khan

Tyrannosaurs may have

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Side Gore

stalked far more of the globe than previously thought. Scientists have found the first

evidence of an ancestor of Tyran- nosaurus rex in the Southern Hemisphere. The discovery may shed light on tyrannosaurs’ evo- lutionary lineage, which many scientists had thought was re- stricted to the Northern Hemi- sphere after the continents began to separate. Tyrannosaurs had previously been documented only in Asia, Europe and North America, but a hip bone discovered in Australia

could have come only from a small tyrannosaur, researchers have concluded. They described their finding in a paper published in the journal Science. The dis- covery raises questions about how and why the two-legged car- nivores evolved to become domi- nant predators above the equa- tor, and why they may have failed to do so below it. “We think tyrannosaurs be- came global early in history,” said

REUTERS

This is the first tyrannosaur fossil found south of the equator.

lead author Roger Benson, a pale- ontologist at the University of Cambridge, “but for some reason, in the north tyrannosaurs be- came exceptionally successful predators — and in the south, they just dwindled away.” The bone was uncovered by pa- leontologist Thomas Rich in 1989 at Dinosaur Cove in Victoria, Australia, along with hundreds of other fossils from a variety of spe- cies. Last year, Rich took them to Benson and other colleagues at the Natural History Museum in London and Museum Victoria in Melbourne, to see if they could identify any of the fossils. This new dinosaur was much smaller than T. rex — probably about 175 pounds and 10 feet long as opposed to T. rex’s four tons and 40 feet. The new tyrannosaur has not

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yet been fully described. It ap- pears to share some basic charac- teristics with the similarly primi- tive northern ancestors of T. rex that lived 110 million years ago, about 40 million years before T. rex first stalked the Earth. University of Maryland tyran- nosaur expert Thomas R. Holtz Jr. said the more-primitive spe- cies focused on small- to mid- sized prey, calling them “the jack- als of the early part of the age of dinosaurs.” Once larger predators died off in the Northern Hemisphere, the tyrannosaur lineage was free to evolve into larger predators, Holtz said. Why a similar evolu- tion didn’t occur in the Southern Hemisphere — and why tyranno- saurs have not previously been seen below the equator — is a mystery. “These are mostly the unwrit- ten chapters of dinosaur history,” Holtz said. “We really don’t have much of a clue as to what Austral- ian dinosaurs were like at the time.”

— Los Angeles Times

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