Bird Abundance and Diversity Increase in Colorado River Delta after Pulse Flow

*Este artículo también fue escrito en inglés. Se puede encontrarlo aquí: La Abundancia y la Diversidad de las Aves Aumentan en el Delta del Río Colorado después del Flujo Pulso.

Late in 2012, the United States and Mexico made a bold move by adopting Minute 319, an innovative agreement to change how Colorado River water is managed at the border. Included were provisions to share Colorado River water surpluses and shortages, and to incentivize water conservation (especially keeping more water in Lake Mead). These measures look more important than ever as we approach the first-ever declared shortages on the Lower Colorado. Provisions in the agreement also required Mexico and the United States to collaborate with environmental NGOs. Over the last few years, Audubon joined forces with Raise the River, a coalition of conservation NGOs. Back in 2012, the Raise the River coalition piloted the first-ever deliberate water deliveries into the long-dry Colorado River Delta for environmental benefits.

Through the 5-year term of Minute 319, more than 150,000 acre-feet of water was sent into the Delta. Some of that water went directly to restoration sites to ensure the staying power of newly planted native trees. Most of the water was delivered as a “pulse flow,” engineered to mimic the natural cycle of spring snowmelt that created vast riparian forests and wetlands in the pre-development Delta ecosystem.

Now, one year after the end of Minute 319 (and the extension of its measures under a new agreement known as Minute 323), the U.S. and Mexican sections of the International Boundary and Water Commission published conclusions of a binational science team that monitored impacts, comprised of federal, university, and NGO researchers. Audubon helped lead these efforts with binational conservation partners.

Here are the key takeaways from the Environmental Report:

Birds: Water is an essential habitat component for birds in the Colorado River Delta, where the river forms a narrow ribbon of green cutting through the Sonoran Desert. Because water is so rare in this region, it’s considered the waistline in the hour-glass shape of the Pacific Flyway. Conservation target birds responded immediately to the pulse flow, including: Albert’s Towhee, Ash-throated Flycatcher, Blue Grosbeak, Black Phoebe, Black-tailed Gnatcatcher, Cactus Wren, Crissal Thrasher, Gila Woodpecker, Hooded Oriole, Ladder-backed Woodpecker, Song Sparrow, Vermillion Flycatcher, Verdin, Western Kingbird, and Yellow-breasted Chat. Scientists monitored the bird response by surveying the river corridor year over year in the spring, before and during the 2014 pulse flow.  They found that during the year of the pulse flow, target bird abundance increased by 20% and diversity increased by 42%. Bird abundance was reduced in subsequent years, but their numbers were still 75% higher in 2016 than in 2013. At irrigated habitat restoration sites, in 2017, bird diversity was 27% greater than the rest of the flood plain while the abundance of the 15 indicator species was 80% higher.

Plants for Birds: The ribbon of green created by plants on the Colorado River in its Delta changed in two notable ways during the term of Minute 319. First, the pulse flow gave existing plants a big drink of water, producing a 17% increase in greenness throughout the river corridor in 2014 compared with 2013.  However, in subsequent years (from 2015 to 2017), plant greenness steadily declined, eventually falling to or below 2013 levels. But local conservation organizations started hand-planting and irrigating hundreds of thousands of new native trees on more than 1000 acres along the river.

Colorado River to the Sea: Sometimes called “a river no more,” the Colorado River was brought to its knees by extensive development of dams and water use through the 20^th century. In most years since the completion of the Glen Canyon Dam (1966), the river did not flow through the Delta. A binational team of scientists and federal agency operations staff designed the pulse flow to be a large, measurable event to enable collection of hydrologic and ecologic data. The binational collaboration significantly advanced knowledge about how water moves through the Colorado River in this region and how water supports the ecosystem. The pulse flow was just enough to reach all the way to the Upper Gulf of California.

Binational Cooperation: It’s worth noting that a team from the United States and Mexico, of federal agencies, scientists, and experts, report these results. This collaboration—of geomorphologists, hydrologists, ecologists, ornithologists, and more—tracks the impacts of habitat restoration efforts in the Colorado River Delta and gives us new knowledge that will help future restoration efforts. Moreover, the blossoming capacity of the United States and Mexico to work collaboratively provides a hopeful sign that the two countries are committed to cooperative, sustainable management on the Colorado River. That’s a very important development, for the birds who need habitat in the once-neglected delta, and for all 40 million people who depend on water from the Colorado River to keep our communities thriving.

Community Connections: While the Minute 319 monitoring agenda did not include social science, the report notes the impact on local communities when the river re-appeared because water was delivered to the Colorado’s channel in the delta.  Recreational opportunities in the Mexicali Valley are few and far between, and water-based recreation is rare. Building connections for the community to the river will be essential to sustain restored habitats in the long run.

The lessons learned from these initial efforts to re-water the Colorado River Delta will be used going forward as Audubon works with Raise the River and the federal governments to implement Minute 323. Continued cooperation between the United States and Mexico appears to hold great promise for the birds, wildlife, and communities both near and far that depend on the Colorado River.