New Audubon Science Doubles Estimates of Shorebird Use in the Colorado River Delta

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On a median day throughout migration, some 250,000 shorebirds might be discovered within the wetlands of the Colorado River Delta—twice earlier estimates. That is in keeping with new science from the Nationwide Audubon Society and Pronatura Noroeste, printed right now in Waterbirds: The Worldwide Journal of Waterbird Biology.  

The study discovered that, for at the least 10 shorebird species, the variety of birds within the Delta on a typical day throughout migration was at the least 1 % of their total hemispheric inhabitants, a key benchmark for designating a web site as a Panorama of Regional Significance by the Western Hemisphere Shorebird Reserve Community. For some shorebird species, the overall percentages throughout a complete migration season are staggering. Factoring within the occasional turnover of migrating people, it’s doable that the Delta helps 12 % of the worldwide Western Sandpiper inhabitants, 20 % of the world’s American Avocets, and an astonishing 24 % of Lengthy-billed Dowitchers and Lengthy-billed Curlews. 

As soon as an unlimited floodplain sustained by the mighty Colorado River, the Colorado River Delta in the course of the Sonoran Desert in Mexico has lengthy been an important lifeline for thousands and thousands of birds—breeding, wintering, and stopping over on their epic journeys throughout the Western Hemisphere. Whereas its significance to landbirds has only recently been revealed, the Delta has lengthy been acknowledged as one of many hemisphere’s most crucial stopovers for migratory shorebirds.  

This research—with help from the LightHawk Conservation Flying and Jonathan Vargas Vega (aerial observer)— additionally recommended that, after accounting for turnover, greater than one million shorebirds could go by the Delta every season. This solidifies the Delta’s place amongst North America’s most crucial migratory stopovers for this imperiled group—a bunch that, in keeping with the 2025 State of the Birds Report, has extra Tipping Level species than another in North America. 

The findings are each a triumph and a warning. They affirm the Delta’s huge ecological worth whereas highlighting its fragility. As soon as nourished by a river that flowed freely to the ocean, greater than 90 % of the Colorado River’s delta habitats have been misplaced to upstream dams and diversions, long-term drought, and an more and more arid local weather. Right now, shorebirds rely closely on wetlands sustained by agricultural runoff and a really small quantity of environmental water releases provided by the USA, Mexico, and a binational coalition of non-governmental organizations. As international change tightens its grip, the way forward for these habitats—and the birds that rely on them—hangs within the steadiness. 

Counting Shorebirds by Sky and Floor 

To gather information for the research, shorebird counters carried out 9 airplane surveys between 2021 and 2023 to disclose the complete scope of the Delta’s significance. They flew over key wetlands and estimated shorebird abundance whereas floor groups recorded and verified species composition and habitat circumstances. Aerial surveys provided a sweeping view, whereas floor observations at choose websites offered a essential correction issue for species composition throughout the broader survey space. 

The outcomes confirmed what conservationists had lengthy suspected: shorebirds focus in areas wealthy in mudflats and shallow water, notably within the southern portion of the Ciénega de Santa Clara the place brackish water mixes with the tides earlier than draining into the Higher Gulf of California. These findings reinforce the pressing want to guard the inflows that provide these wetlands. With out a dependable supply of water, these essential habitats—and the numerous birds that depend on them—might vanish. 

A Fragile Stronghold 

Traditionally, the Colorado River’s delta was an unlimited wetland system of practically two million hectares that ebbed and flowed with seasonal snowmelt from the Rocky Mountains to the north. Right now, greater than 90 % has been misplaced. The Ciénega de Santa Clara—at 40,000 acres the Delta’s largest remaining wetland—survives due to an unlikely supply: agricultural wastewater from the USA, which supplies 90 % of its water. 

“For all its ecological worth, the Ciénega exists in fixed uncertainty,” stated lead researcher Tim Meehan. “It’s a thriving wetland, however its water supply just isn’t protected. That makes it extremely weak to adjustments in water administration insurance policies.” 

One risk that has loomed for years is the doable reactivation of the Yuma Desalting Plant, a U.S. facility designed to deal with the agricultural water runoff that provides the Ciénega and ship it to irrigate farms. The Yuma Desalting Plant, constructed within the late 1980’s, was operated for lower than two years and right now is a long-abandoned facility with previous expertise that might take thousands and thousands of taxpayer {dollars} to restore and extra to function. If operations restarted, the water that feeds the Cienega could be diverted to this plant with vital implications for shorebirds and their habitat.

Securing a Future for Shorebirds 

Shorebirds don’t acknowledge borders. Many species that rely on the Delta breed within the Arctic migrating by North America and wintering as far south as Central and South America. Defending them requires collaboration throughout worldwide boundaries, from breeding grounds to stopover websites to wintering habitats. 

One mannequin for such cooperation is Minute 323, an settlement beneath the 1944 Colorado River Treaty between the USA and Mexico that has helped restore modest environmental flows to the Delta however doesn’t tackle flows for the Ciénega. Whereas a essential step, specialists warn that rather more have to be executed to make sure the Delta’s wetlands endure. 

“This analysis makes it clear that water for wildlife must be a precedence in future administration choices,” Meehan stated. “1 / 4-million shorebirds on any given day throughout migration—and probably one million over a season—rely on it.” 

In response to Stefanny Villagomez, wildlife biologist at Pronatura Noroeste, the research’s findings spotlight a essential alternative.  

“The outcomes of this research present key information to assist promote regional water administration insurance policies targeted on conservation, which might safe the way forward for this very important ecosystem for the survival of migratory shorebirds, particularly given the present human water calls for and local weather change,” Villagomez stated. As human calls for and local weather pressures intensify, the Colorado River’s destiny grows ever extra unsure. With out sustained water, the Delta’s wetlands will proceed to shrink—with them, one of many Western Hemisphere’s most crucial waypoints for migratory shorebirds. 

For these outstanding vacationers, the Colorado River Delta is excess of a relaxation cease—it’s a keystone of their migratory journey. Safeguarding its future means preserving the interconnected net of life that is dependent upon this vanishing river. 

For extra data on shorebird migration, please go to the Bird Migration Explorer.