Sandhill Cranes' Migratory Tales

Banding Program Collects Key Data

The tracking information may help predict how many cranes the Platte River Valley can support

Story by
Julie Anderson

Photos by
Jeffrey Z. Carney

Article taken from The Omaha World-Herald, Wednesday, March 31, 1999

The morning passed quietly for the three men lying in wait on the edges of a cow pasture--one crouched behind a cedar tree, two others sitting in pickup trucks. Skies were sunny, the breeze mild, but few sandhill cranes were flying. Then a group of seven dropped into the field, wings waggling like an airplane's, drawn in by 10 taxidermy mounted decoys. A crackle of hand-held radios. A countdown. Boom. Three hidden rockets fired and cast a net over a family of three cranes like a blanket, trapping the struggling birds. The three men raced in, put the birds in burlap bags to calm them, drew blood samples, recorded data and fastened a satellite transmitter around the adult male crane's leg. Standing in a line, the men carefully took the hissing, nipping birds from the bags, stroked their feathered chests and released them to climb back into the air and glide away.


		FUTURE BAND MEMBERS: At left, a captured crane, placed in a bag to calm its nerves, snaps at a wildlife biologist trying to release it. The capture, banding and release takes only 15 minutes so the banded cranes can join others, such as one flying past the moon, above.

Monday's capture, banding and release took only 15 minutes. But the information that these birds and others are unwittingly providing is expected to give researchers and habitat managers the most detailed report ever on the migrations of sandhill cranes. Ultimately, the researchers hope to use information gathered in their studies to develop a mathematical model that can help predict how many cranes the Platte River Valley can support now, and what management steps could improve the habitat. The open river channels the birds prefer have been shrinking, crowding the birds into a smaller area, making it more difficult for them to find adequate food.

During its stopover along the Platte, the midcontinent flock makes up the world's largest concentration of sandhill cranes. Researchers want to learn more about where, and under what conditions, different groups of cranes spend their time during the rest of the year. The timing of the northern and southern migrations and the factors that influence them also are on the researchers' list for study, along with gaining insight into how many birds make up the midcontinent flock. Roughly a half-million cranes pass through the Platte Valley each spring. Another goal of the work is to determine whether cranes can still find enough food in the Platte Valley to store the fat and nutrients they need to migate north and nest.

The satellite telemetry also should help scientists determine the birds' habitat needs through the year, no matter where they are, said Gary Krapu, a research biologist with the U.S. Geological Survey's Northern Prairie Wildlife Research Center in Jamestown, N.D. The studies, part of a larger investigation into how best to manage the Platte River, make up the most comprehensive work on sandhill cranes since Krapu followed them in the 1970s. It's also the first to use satellite telemetry on cranes. The work already is turning up interesting findings.

Last spring, researchers captured and attached satellite transmitters to five sandhills in the Platte Valley. Two of those five birds later crossed the Bering Strait and spent the summer in Siberia. That information was unexpected, Krapu said. Researchers knew some sandhills spent the summer in Siberia, but they thought the birds came from another flock, not the midcontinent group.

Last fall, the two birds--which had nested 200 miles apart in Siberia--flew 4,200 miles south to wintering grounds along the Gulf of Mexico, arriving in Texas within two days of each other. All five birds tagged with satellite transmitters arrived within six days, even though they'd ranged from Siberia to Hudson Bay. Krapu hopes to learn more about the factors controlling the timing and patterns of the cranes' migration. Cranes, unlike most other birds, often ride air currents in migration and may be particularly sensitive to weather. "If they time migration right, they get a huge lift from air currents, which really reduces the amount of energy they have to spend during migration," he said.

The researchers planned to tag 16 more birds this spring and at least 40 more next year with a goal of tracking 200 birds. The scientists want to find out where the three subspecies--greater, intermediate and lesser sandhill cranes--and smaller groups spend their time on the Platte along with identifying their breeding and wintering grounds.

The male bird the scientists captured Monday was No. 15 for this year, said Dave Brandt, a wildlife biologist with the Northern Prairie center who has been working with Krapu on the Platte. Brandt planned to try to net the last bird Tuesday near Overton, on the western edge of the birds' rest stop on the Platte. Each satellite transmitter weighs about an ounce and has a 10-inch antenna. The transmitter is attached to a two-inch-long plastic leg band that fits above the bird's knee. The transmitters have about 1.25 years of transmitting time, allowing biologists to track the birds from the Platte, north to the breeding grounds, south to the wintering grounds and back to the breeding grounds again.

Catching sandhill cranes is no easy task. The biologists scout a location--usually a pasture with nearby water--where cranes like to loaf at midmorning after feeding awhile in the fields. Brandt hides the net and rockets the night before. Before the cranes arrive, he stakes out the mounted cranes within the throw of the net to draw in his quarry. "These birds are awful wary," he said. Brandt, dressed in camouflage, hides out nearby and when the right birds--usually a family group--land in the right spot--not too close or too far from the net--he trips a remote control and fires the rockets.

FAUX CRANES: Lifelike sandhill crane decoys are placed by wildlife biologist Dave
Brandt in a meadow near Grand Island to attract other cranes so that they can be
captured and banded with a global-positioning transmitter to gather migration data.

Monday, Brandt worked quickly with Tom Buhl of the Northern Prairie center and Wade Jones, a seasonal worker there, to process and release the birds before they became too stressed. On some birds, the biologists also have attached short-range radio transmitters that they can follow from the ground, repeating work done in the 1970s. Ten birds got radio transmitters last year, programmed to turn on this spring when the birds arrived back at the Platte. Of those 10, the biologists have picked up and are monitoring signals from five--two of which are accompanied by young birds.

As part of their work, the researchers also are documenting how much time cranes spend searching for different kinds of food and how much waste corn is available in fields. About 100 cranes were taken last year--along with a similar number this year--to allow biologists to compare their fat levels, again repeating Krapu's work in the 1970s. Researchers found then that the Platte Valley is the primary location where the cranes store fat for migration and breeding.

The researchers have found that the cranes spend as much time finding invertebrates in grasslands and wet meadows--earthworms and beetle larvae--for the 3 percent of protein that makes up their diets as they spend getting corn that makes up the other 97 percent. The protein eventually goes into making eggs. The studies also indicate that the amount of corn available is declining, possibly because of more efficient combines or competition from growing flocks of geese. Cranes are ranging farther from the river to find food, Krapu said, and they might be having greater difficulty putting on fat.

However, results aren't available yet to determine whether spending more time looking for food has affected their physical condition, he said. Last year, fat levels were the same as in the 1970s. Other researchers also have been working with the North Dakota scientists on their own studies, including looking at the birds' reproductive health and whether cranes are carrying environmental contaminants.