Larger Flocks of Whooping Cranes Pose Survival Risks

(CN) — Fewer wetlands in the Great Plains have contributed to larger flocks of endangered whooping cranes during migration cycles, a phenomenon that could benefit the bird’s recovery or intensify risks from extreme weather and disease outbreaks, according to a study released Thursday.

Using sightings data collected by the U.S. Fish and Wildlife Service, a team of researchers found whooping cranes have started assembling in flocks as large as 150 while making annual treks from Texas to Canada. It’s a stark departure from flocks that rarely exceeded nine to 12 birds, researchers found in a study published in the journal Heliyon.

Whooping crane chick with puppet. (Jonathan L. Fiely / USGS Patuxent Wildlife Research Center)

“We found groups are increasing in size regardless of how you measure it,” said Andrew Caven, co-author of the study. “There’s evidence to suggest that limited wetland availability was contributing to this.”

More than 500 North American whooping cranes exist in the wild today. The number of whooping cranes dropped as low as 16 in the 1940s due largely to overhunting. Conservation efforts, including raising cranes in captivity and using ultralight aircraft to teach them how to migrate south for the winter, have been credited with bringing the birds back from the brink of extinction.

“Whooping crane conservation is one of North America’s great success stories,” Caven said.

The whooping cranes migrate each spring from their wintering grounds in Aransas National Wildlife Refuge in Texas to their breeding grounds in Wood Buffalo National Park in Alberta, Canada.

By gathering in larger groups during pit stops on the 3,000-mile journey, the birds can more easily signal each other about dangers, such as predators, and forage at higher rates.

However, larger groups also carry greater risks. A hailstorm or disease, such as avian cholera, could wipe out a fifth of the population in one fowl swoop, according to U.S. Fish and Wildlife biologist Matt Rabbe, who co-authored the study.

“Larger congregation of whooping cranes increases the potential for a catastrophic loss from disease or something along those lines, particularly when you have a small overall population size,” Rabbe said.

In setting out to understand why whooping cranes started flocking together in larger numbers, researchers found fewer wetlands likely play a major role. Larger flocks of migratory birds were found most frequently in the Southern Great Plains, where wetland habitats are sparse but a few high-quality wetlands remain, Caven explained.

“The Great plains used to be one of the largest grassland ecosystems in the world,” Caven said.

A rise in agriculture, land development, drought and climate change have all worked together to substantially reduce wetlands in the region, according to Caven and Rabbe.

Efforts to reverse that trend are ongoing. Provisions in the Farm Bill offer financial incentives to farmers who restore former wetlands on sections of their land where it is typically harder to grow crops, Caven explained.

The National Wildlife Refuge System can also acquire and restore wetlands in the Southern Great Plains. Additionally, partnerships between conservation groups and government agencies can help scientists learn more about endangered whooping cranes and how to best prioritize resources.

“The more we can learn about them, the better we can manage for them,” Rabbe said. “We know when they’re migrating, where they’re migrating, and what types of resources they need. That will help us manage for recovery.”

The Endangered Species Act also protects wetlands that serve as essential habitat for whooping cranes. Environmentalists have argued that projects like the Keystone XL oil pipeline threaten the bird’s survival because an oil spill could contaminate their feeding and resting locations. A federal judge also relied on that law last year when ordering Trump administration to reconsider how relaxed renewable fuel standards will affect endangered species such as the whooping crane.

For those who want to help endangered whooping cranes, Caven recommends supporting land trusts in the Southern Great Plains that are working to acquire, restore and conserve bird habitats.

Following up on this study, Caven’s research team plans to investigate if whooping cranes are spending more time at certain locations during their migration, and what factors might contribute to longer stays at certain stops. This will help determine which sites are most essential in providing resources during their long journeys.

The whooping crane is the tallest bird in North America, growing to five feet tall with a wingspan of up to seven feet. They can live 20 years or longer in the wild. They are omnivores, feeding on berries, sedge roots, grains, fish, frogs and crayfish. Bald and golden eagles, bobcats, coyotes and wolves are among their natural predators. They are still endangered.

Costumed care taker training whooping crane chick to follow the Ultralight. (USGS photo)
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