This article was written by Eduardo González‑Sargas, a Colorado State University research scientist and ecologist whose work focuses on river and restoration ecology.
For more than a decade, the Raise the River coalition, including the National Audubon Society, has worked in collaboration with the United States and Mexico under the framework of Colorado River Treaty agreements (Minutes 319 and 323), to bring back healthy habitats in the Colorado River Delta. Working from my perch at Colorado State University with support from Audubon as well as federal funding, and with partners in Mexico and the United States, I led a series of studies to find out whether those efforts are actually helping birds. The short answer is yes, and in meaningful ways.
Bird surveys at 230 sites across the delta, carried out from 2002 to 2021, paint an encouraging picture: over those 20 years, researchers counted more than 100,000 individual birds. In areas where native trees and shrubs such as cottonwoods, willows, and mesquites were planted, birds that depend on riverside forests, like Abert’s Towhee, Song Sparrow, and Yellow-breasted Chat, started showing up in greater numbers. Perhaps even more surprising, bird populations in nearby areas that weren’t directly restored also stopped declining, suggesting that restoration can have a ripple effect across the landscape.
So what makes a good bird habitat in the Delta? The first study, published in Ecological Engineering, found riverside forest breeding specialists are found almost exclusively in replanted areas. A few wetland bird species such as American Coot and Marsh Wren were found near remnant open water and marshes. On the flip side, invasive plants like tamarisk and bare, barren ground tend to push nearly all birds away. Farmland did attract some birds too, particularly adaptable, generalist species: Mourning Dove, Red-winged Blackbird, Great-tailed Grackle.
A second study, published in Journal of Arid Environments, looked more closely at how different groups (or guilds) of birds responded. Birds that specifically need riverside forest habitat thrived most in the wetter, more established restored areas. In drier zones where restoration started more recently, those same birds are improving too, just more slowly, which makes sense given that young forests take time to grow. Wetland birds benefitted in the wetter areas, while desert-adapted species such as Greater Roadrunner, Lesser Nighthawk, and Loggerhead Shrike were most common in the driest parts of the delta. Generalist birds were plentiful everywhere, but actually decreased a bit after replanting, showing that restoration is doing its job of bringing back more specialized wildlife.
The third study, also in Ecological Engineering, tackled a trickier question: how do you actually measure whether restoration is working? It turns out the answer depends a lot on what you’re measuring. Of the 163 bird species detected across the Delta over 20 years, the analyses focused on the 53 species confirmed to breed there, since sampling protocols were not designed for migrants. When my partners and I looked at overall bird diversity across a river reach, the numbers didn’t always go up, not because restoration wasn’t working, but because some areas with remnant riverside forests and marshes had concentrated the remaining populations of breeding birds before restoration began, masking the gains. Looking at individual species and bird groups told a much clearer story. To figure this out, it was necessary to combine analyses at the community, guild, and species level to fully understand bird response to restoration.
Among the 30 most common breeding birds in the Delta, the results were mixed but hopeful. Ten out of 16 riverside forest specialist species were detected more often in restored areas in the wetter parts of the delta. Species like Abert’s Towhee, Ash-throated Flycatcher, Blue Grosbeak, Song Sparrow, and Yellow-breasted Chat all responded well to replanting. A few others, including the Western Kingbird and Black-tailed Gnatcatcher, didn’t show the same improvement, and researchers aren’t yet sure why, which opens the door for future study.
All of this matters beyond the Delta itself. The United States and Mexico are expected to negotiate a new binational Colorado River water-sharing agreement in 2026, and this research gives decision-makers concrete guidance on where and how to focus restoration efforts for the greatest benefit to wildlife. And the lessons learned here: about which plants attract which birds, about how long recovery takes for each species, about which indicators actually capture progress, can be applied to degraded rivers and floodplains around the world.
The Colorado River Delta is proof that targeted restoration works. With continued investment and the right science guiding the way, the Delta’s birds and the ecosystem they depend on have a real chance to recover.
