The marvel of the cranes

WOOD RIVER, Neb. — Like clockwork each spring, sandhill cranes arrive in Nebraska in one of the world's great migration spectacles.

Now biologists are learning more about what makes cranes tick.

A new report by Wood River-based researchers reveals a dynamic weekly pattern in which cranes select Platte River roosting sites when they fly into south-central Nebraska.

In Interstate 80 traveler terms, late-arriving cranes select low-rent hotels in exchange for spending more of their vacation time in four-star restaurants.

In another finding, although cranes appear to filter in and out of Nebraska during an eight-week staging period, they come and go in three apparent waves rooted to three geographic wintering and breeding areas.

“Nebraska and the Platte River is a unique place in the world for migratory birds,” said Dr. Karine Gil, a crane population ecologist at the Crane Trust. “Many people have no idea what's happening on the Platte River. It's beautiful.”

The findings are part of report on an 11-year study compiled by Gil and Dr. Felipe Chavez-Ramirez, executive director of the Crane Trust and an avian ecologist. Their report will be published in Waterbirds, an academic journal.

Hundreds of thousands of sandhill cranes arrive in Nebraska from late February through mid-April. Individual birds rest and feed for two to four weeks along the Platte River from Chapman to Overton.

The staging allows the birds to forage and accumulate fat that will provide them with energy for their migration to Arctic breeding grounds.

The leading wave of cranes — those arriving now — invariably zero in on a 12-mile stretch of the Platte between Grand Island and Wood River. Up to half of the cranes arriving in Nebraska during the first two weeks of the migration roost in a seven-mile stretch from Grand Island to Alda, Gil said.

During the following several weeks, cranes progressively will expand their roosting areas to a few miles east of Grand Island and west to Gibbon — claiming a 33-mile stretch of the Platte.

By the end of spring migration, most Platte roosts will stretch across about 60 miles from Chapman west to Odessa. During the final three weeks of staging, a higher proportion of cranes are typically found in the Kearney and Odessa areas, Gil said.

Although newly arriving cranes appear to roost close to earlier arriving birds, they unfailingly spread into sites with less favorable habitat, Gil said. These shifts to other river segments may not be related to roost habitat as much as nearby feeding sites.

“The large numbers of cranes in the first roosts ... may have reduced food availability in the surrounding areas,'' Gil said.

The depletion of those areas would lead later arrivals to select roost locations farther west, where waste corn is more abundant in harvested fields, she said.

In other words, a good place to dine trumps a swank place to spend the night.

Gil said other researchers say a number of factors, including age, breeding needs and the availability of roost habitat may explain why cranes arrive in three apparent waves.

Although it's almost impossible for most people to distinguish differences, sandhill cranes passing through Nebraska are made up of three subspecies: lesser, greater and Canadian.

Lesser cranes, the most abundant, winter in Arizona, New Mexico and the Texas Panhandle and breed in western Alaska and Siberia. They appear to stage mostly in the Kearney area and along the North Platte River in western Nebraska.

Greater cranes winter along the Texas Gulf Coast and stage primarily along eastern portions of the Platte near Grand Island.

Canadian cranes winter in Mexico and the Texas coast and breed in east-central Saskatchewan. Gil said it's difficult to generalize where they stage.

The breeding cycle is a second possible explanation of the three waves, Gil said.

Breeders may arrive first in Nebraska and gain enough energy in a short time (two weeks) to continue migration. The later arrival and longer staging of younger cranes may result from their lack of urgency to breed.

Previous studies have noted a significant shift in the number of roosting sites eastward from the Kearney area toward Grand Island since 1957.

Cranes apparently are responding to areas cleared of trees and other woody vegetation by the Audubon Society and other organizations, Gil said.

Since the 1970s, the Platte upstream from Kearney generally has been unsuitable for crane use because of heavy vegetation and choked river channels, Gil said, but some cranes have responded when isolated sections have been cleared by staging near Elm Creek.

Gil said roosting areas skipped by the cranes should be studied to determine whether isolated sections could be cleared for staging in the future when crane populations could be higher.

The average peak crane population in Nebraska during the study period was 300,000 birds. Last year's peak of more than 400,000 cranes occurred in the last two weeks of March.

The Crane Trust is a nonprofit organization created to protect and enhance habitat for cranes and other migratory birds along the Big Bend region of the Platte. It recently shortened its name. It had been known as the Platte River Whooping Crane Maintenance Trust.

Contact the writer:

444-1127, david.hendee@owh.com

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