Discovery of Hidden Groups Within Migratory Shorebird Could Aid Conservation

Tracking Data Revealed Three Groups of Long-Billed Curlew, Each With Unique Migration Patterns and Conservation Needs

Researchers at the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) have uncovered three distinct groups of long-billed curlews, a North American migratory shorebird facing significant population declines.  

The results, published today, March 13, in the Journal of Applied Ecology, show each group has its own unique set of migratory routes and key stopover sites. Elly Knight, who led the study as a postdoctoral fellow at NZCBI and is now a statistical ecologist and adjunct professor at University of Alberta, said the distinct groups may face different threats depending on their migration route and favorite places to rest and refuel along their journeys.   

“This research demonstrates the power of tracking data for capturing the full annual cycle of migratory birds and how important that is for conservation,” said Knight, who was co-advised by Autumn-Lynn Harrison, NZCBI research ecologist and last author on the study, and Jay Carlisle, research director at Boise State University’s Intermountain Bird Observatory. “By identifying distinct groups of curlews with different needs and population trends, we can tailor conservation efforts to each group. The goal is to link the different population trends with specific threats the birds face along their respective migration routes. Without that information, we can’t effectively intervene to protect them.” 

North America’s largest shorebird, the long-billed curlew, is considered a species of conservation concern due to habitat loss and degradation. While curlews breed primarily in the Canadian prairies and the Great Plains and the Great Basin in the U.S., their winter habitats vary widely. The species is known to overwinter along the Pacific and Gulf coasts, and there is a small and vanishing population that winters along the southeastern coast of the U.S. However, long-billed curlews also use interior areas such as grasslands and wetlands from Texas across to California and in Mexico.    

Until now, conservation efforts have overlooked crucial nuances in the ecological needs and population trends of these three groups of curlews. Between 2007 and 2021, 14 different research groups, including NZCBI, used satellite tags to track 130 long-billed curlews from across their entire North American range in Canada, the U.S. and Mexico.  

In addition to answering important conservation questions, this synthesis places data for each researcher and study area into a larger context of long-billed curlew migratory ecology. “Our research groups worked together to share data, tags and capture techniques,” Harrison said. “We even joined one another in the field, showing the power of collaborative science in a technological age.”  

The advent of new tracking technology is changing the way scientists study and understand migratory species. Prior to this, researchers relied on recapture data, bird banding and observation on the ground. Now, they can follow numerous individuals throughout the year, even in the air. 

To find patterns in this dataset, researchers analyzed the data with an algorithm designed to clump the birds into groups based on the similarity of their flight paths—a concept known as migratory connectivity, which is an estimate of how cohesive a population is across its annual cycle. Next, the team examined the population trends, movement behaviors and habitat preferences for each of the resulting groups and found three distinct populations of curlews: a western group that migrates approximately 1,600 kilometers, an intermountain group that migrates 2,000 kilometers and a plains group (eastern) that migrates 3,000 kilometers. Each of these groups also showed different population trends between 2007 and 2019. The western and plains groups declined, while the intermountain group increased.  

Harrison said this delineation is critical to understand conservation needs across the range, and Knight hoped that their approach—using migratory connectivity information to identify conservation-relevant groups with unique ecological needs and population trends—can serve as a blueprint for research on other migratory bird species.  

The findings reveal previously invisible differences within long-billed curlews and provide unprecedented resolution on the full suite of habitats and locations the species utilizes during its annual migratory cycle. Of the three groups, the plains group had longer, slower migrations with more stops than the other groups. Notably, all three groups showed a strong preference for agricultural fields as stopovers during migration and during the winter nonbreeding season. These insights could prove useful for conservation efforts. Co-authors plan future work to evaluate the unique threats faced by each of the three long-billed curlew groups identified by the study. 

This research was done as a part of NZCBI’s Migratory Connectivity Project, supported by ConocoPhillips, with many other funding partners, management agencies and landowners contributing to the curlew tracking efforts since 2007. Partners include the NZCBI Great Plains Science Program, Audubon Canyon Ranch, Birds Canada, Coastal Bend Bays & Estuaries Program, Boise State University’s Intermountain Bird Observatory, Field Guides Inc., Georgetown University, Iowa State University, Nebraska Game and Parks Commission, Point Blue Conservation Science, Ricketts Conservation Foundation, Universidad Autónoma de Nuevo León, University of Nebraska-Lincoln, University of Oklahoma and USGS Alaska Science Center.  

 
About the Smithsonian’s National Zoo and Conservation Biology Institute  

The Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) leads the Smithsonian’s global effort to save species, better understand ecosystems and train future generations of conservationists. Its two campuses are home to some of the world’s most critically endangered species. Always free of charge, the Zoo’s 163-acre park in the heart of Washington, D.C., features 2,200 animals representing 400 species and is a popular destination for children and families. At the Conservation Biology Institute’s 3,200-acre campus in Virginia, breeding and veterinary research on more than 250 animals representing 20 species provide critical data for the management of animals in human care and valuable insights for conservation of wild populations. NZCBI’s more than 300 staff and scientists work in Washington, D.C., Virginia and with partners at field sites across the United States and in more than 30 countries to save wildlife, collaborate with communities and conserve native habitats. NZCBI is a long-standing accredited member of the Association of Zoos and Aquariums.  

About the Life on a Sustainable Planet Initiative 

Life on a Sustainable Planet (LSP) is a vital initiative from the Smithsonian designed to advance and inspire global engagement in environmental stewardship. This comprehensive program applies the Smithsonian’s expertise in science, outreach and education to foster holistic approaches to preserving ecosystems, building resilience and educating the world about sustainable climate solutions. Smithsonian scientists partner with communities and organizations around the world, conducting research and educational programs to shape the future. LSP programs save and protect biodiversity, champion sustainable practices and offer innovative solutions to the challenges posed by our changing climate. 

About Boise State University and the Intermountain Bird Observatory 

Boise State provides an innovative, transformative and equitable educational environment that prepares students for success and advances Idaho and the world. Serving more than 32,000 students annually, Boise State is proud to be powered by creativity and innovation, receiving national recognition as one of the most innovative universities in the country. Located in Idaho’s capital city, the university has a growing research agenda and plays a crucial role in the region’s knowledge economy and famed quality of life. In the past 10 years, the university has quadrupled the number of doctoral degrees and doubled its master’s degree offerings. Learn more at BoiseState.edu. 

The Intermountain Bird Observatory's (IBO) mission is “Impacting human lives and significantly contributing to conservation through a unique combination of cooperative research focusing on birds, education, discovery of the natural world and community engagement.” 

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Photo caption: Scientists used small solar tags to identify where long-billed curlews migrate, revealing hidden populations of North America’s largest shorebird.  
Photo credit: Andy Boyce, Smithsonian’s National Zoo and Conservation Biology Institute