WATER POLITICS

A decade-old effort to restore the once parched Colorado River delta in northwestern Mexico appears to be succeeding. Since the United States and Mexico agreed to restore some water to the delta in 2012, populations of native birds and plants have begun to rebound after decades of decline, researchers report in two recent studies.

The results highlight “what can be achieved by establishing a balance in sustainable water management for the benefit of all, including the ecosystems themselves,” says Roberto Alejandro Sánchez-Rodríguez, a climate change specialist at the College of the Northern Border who was not involved in the studies.

Most of the 2300-kilometer-long Colorado River is in the United States. But the river’s final 106 kilometers flow through Mexico to a delta along the Gulf of Baja California. By the early 2000s, researchers estimated the delta had lost 90% of its forests and wetlands because dams and water withdrawals had drained the lower Colorado.

In a bid to reverse those losses, in 2014 the U.S. began to release relatively small but critical flows of water into the delta. At the same time, Mexican and U.S. nonprofit groups launched a restoration effort called Raise The River, which has been working with local communities to restore riverside vegetation and monitor how delta ecosystems are responding to the water’s return.

By 2017, researchers were seeing gains in tree and bird populations, says Osvel Hinojosa-Huerta, a conservation specialist at the Cornell Lab of Ornithology. “It was really impressive how quickly they respond to restoration,” he says.

Now, Hinojosa-Huerta and colleagues have published two studies that detail continued improvement. In one, published in June in Ecological Engineering, the researchers compared how 53 species of birds that breed in the delta were faring in restored and nonrestored areas. The surveys, conducted from 2002 to 2021, showed that in restored areas 60% of the species, including native birds such as Abert’s towhee and blue grosbeak, had stopped declining or were possibly increasing. At the same time, populations of invasive bird species in restored areas declined.

The return of native vegetation is likely one reason the birds are doing better, the researchers report in the second study, also published in June in Ecological Engineering. In particular, the replanting or natural return of native trees and shrubs, as well as removal of non-native tamarisk trees, correlated with healthier bird populations.

María Eustolia López Enríquez, a resident of the delta community of San Luis Río Colorado, says it’s hard to believe how much parts of the delta have changed. Ten years ago, she volunteered to help replant trees in a major reforestation site called Miguel Alemán. Now, she likes to visit the revitalized forest and even give a hug to a favorite cottonwood tree.

The tree “is a great gift,” López Enríquez says. “I take a few minutes to go and admire it and listen to it. … It’s very satisfying to listen to the sound of its leaves in the wind.”

She and others involved in the restoration effort hope it will continue to produce results. In 2017, they note, the U.S. and Mexico agreed to increase the amount of water released to the delta and maintain the flow through at least 2026.