By: Jonathan Vargas 1,3, Stefanny Villagomez-Palma 2, Chad Witko1 and Osvel Hinojosa-Huerta2,3
1National Audubon Society
2Pronatura Noroeste A.C.
3Fellows Coastal Solutions Fellows Program, Cornell Lab of Ornithology
The Alto Golfo de California and Delta de Rio Colorado (Upper Gulf of California and the Colorado River Delta), located in northwestern Mexico, is a Site of Hemispheric Importance by the Western Hemisphere Shorebird Reserve Network (WHSRN). Annually hosting 160,000 shorebirds of 36 species, this region also hosts at least 35% of the roselaari subspecies of Red Knots (Calidris canutus roselaari). Within this wetland system, the Ciénega de Santa Clara (Santa Clara Marsh) is considered the largest and most ecologically important marsh in northwestern Mexico. One example of its ecological importance is that the Ciénega de Santa Clara houses 75% of the population of the Yuma Ridgway’s Rail (Rallus obsoletus yumanensis), a subspecies endemic to the lower basin of the Colorado River that is a priority species for its conservation in Mexico and is in danger of extinction in the United States (US). The Ciénega also supports one of Mexico’s only populations of the California Black Rail (Laterallus jamaicensis coturnicus).
The Colorado River flows through seven states in the United States and two in Mexico. The last 140 km of the river are in Mexico, creating a delta system of more than 400,000 hectares. The human demands for water in this arid region are great, on both sides of the border. The 1944 United States-Mexico Water Treaty ensured that 1.5 million acre-feet of water is delivered to Mexico annually. However, since then, only limited amounts of water has been allocated for environmental purposes in the basin. The Delta has lost 80% of its wetlands in the last century due to the construction of dams, diversions of water for human consumption in the basin, and increase in agricultural activity in the region. The riverbed is dry starting 160 km before reaching the sea. Because of dwindling habitat, there has been drastic decreases in the populations of various species of birds, including Sandhill Crane (Antigone canadensis), Willow Flycatcher (Empidonax traillii extimus), Yellow-billed Cuckoo (Coccyzus americanus occidentalis), and Fulvous Whistling-Duck (Dendrocygna bicolor).
Flock of American Avocet (Recurvirostra americana) resting in the upper estuary of the Colorado River. Photo: Jonathan Vargas.
Despite these impacts, the Colorado River Delta remains a critical site for conservation, due in part to the maintenance of a portion of the wetlands from agricultural drainage flows, underground flows, and treated wastewater. Now water is also directly dedicated to the environment through creative binational negotiations between the two countries.
Two decades ago, academic institutions and non-governmental organizations in the United States and Mexico established a collaborative initiative to study, improve and conserve habitat conditions in this region. Today, thanks to multisectoral participation and the creation of binational government agreements between both countries, especially Minute 323 of the International Boundary and Water Treaty, restoration and conservation activities have been successfully implemented with notable improvements in the conditions of the critical habitat for wildlife in the Delta.
Water users, government agencies, and communities all contributed to the agreements, which resulted in the inclusion of an allocation of water for environmental purposes, especially for the restoration of wetlands and other habitats in the region. Minute 323, which provides a framework for cooperative action of the US-Mexico Water Treaty of 1944, and covers a timeframe from 2017-2026 and a total of 210 thousand acre-feet of water were secured for the environment. This includes the delivery of 35,671 acre-feet between May and October 2021 and 34,860 acre-feet between May 1 and mid-September of 2022. These water flows have helped revitalize riparian and estuarine delta habitats and have allowed the reconnection of Colorado River water with the tides of the Upper Gulf of California.
Since 2021, the National Audubon Society, the Cornell Ornithology Laboratory Coastal Solutions Fellows Program, LightHawk, Pronatura Noroeste A.C., and the National Commission of Natural Protected Areas (Upper Gulf of California and Colorado River Delta Biosphere Reserve) collaborated to implement a monitoring program which will increase understanding of the shorebird community that uses the areas of the upper estuary and the Ciénega de Santa Clara during the fall and spring migrations. This effort seeks to assess the impact of freshwater flows in the estuarine zone of the Delta to help refine the strategies of restoration in the area. This includes the design of the water delivery in the river, as well as the implementation of hydrological connectivity works.
Left: Aerial survey team. From left to right: Stefany Villagómez, Chuck Scroll (pilot) and Jonathan Vargas. Right: Monitoring team in the Colorado River Delta. From left to right and from top to bottom: Juan Carlos Medina, Juan Butrón Méndez, José Juan Butrón, Miguel Ángel Cruz, Bernabe Rico Hurtado, Benito Rocha, Alejandra Calvo Fonseca, Jonathan Vargas and Stefanny Villagómez-Palma.
The shorebird surveys were carried out simultaneously by air and on the ground in the lower Colorado River Delta, covering a total of 40,000 hectares. The main objectives of the surveys is to estimate the total number of birds present in the study area, identify the areas with the greatest abundance of birds, evaluate habitat changes with water flows, and to provide specific information on the richness and composition of the shorebird species present during each season.
So far ten surveys have been conducted, documenting the presence of 23 species and up to 34,000 migratory shorebirds per season. Small birds (e.g., Calidris spp., Charadrius spp., and Phalaropus spp.) account for up to 70% of all birds present in the Colorado River Delta during migration. The area with the greatest abundance of shorebirds is located in the muddy plain of the southern part of the Ciénega de Santa Clara, where the waters of agricultural return are mixed with the tides of the Upper Gulf. In this area of the Ciénega, flocks of up to 13,000 shorebirds were recorded, with dominance of Western Sandpiper (C. mauri) and other small species. Additionally, one of the most significant results is the documentation of important groups of shorebirds in the Upper Estuary area, where restoration is ongoing and the allocation of environmental flows is improving habitat conditions. The aerial surveys also documented the connection of the river waters with the tides in the estuary in an area of approximately 8,000 hectares.
Location and abundance of shorebirds in the DRC during the air censuses during spring migration 2022
In addition to documenting the use of these habitats and contributing to shorebird population research, the comparison of census results spatially and over time will increase understanding of the effectiveness of the conservation actions implemented, and the habitat conditions needed to ensure the well-being of shorebirds and local communities that depend on the site. This information will be included in the restoration strategies of the Colorado River Delta Estuary in a binational context and will be used in decision-making on the allocation of environmental flows in subsequent years.
Shorebirds seen from the air in the Ciénega de Santa Clara. Photo: Jonathan Vargas
Acknowledgments
Christine Steele, Audrey Ek-Psomas, Bill Rush, Chuck Scroll, Ray Lee, Will Worthington (LightHawk), Joey Kahn, Tim Meehan (National Audubon Society), Eduardo Soto (CONANP), Miguel Vargas, Alejandra Calvo, José Juan Butrón, Juan Ángel Butrón, Juan Butrón, Benito Rocha, Juan Carlos Medina, Dilan Ortiz, Francisco Castillo (Pronatura Noroeste A.C.), and the Neotropical Migratory Bird Conservation Act (NMBCA) program.
Additional Resources
Hinojosa-Huerta, O., S. DeStefano, & W. Shaw. 2001a. Abundance and distribution of the Yuma Clapper Rail (Rallus longirostris yumanensis) in the Colorado River Delta, Mexico. Journal of Arid Environments 49:171-182.
Official Journal of the Federation. 2019. Modification to A nexus Normativo III, List of species at risk of the Official Mexican Standard NOM-059-SEMARNAT-2010, environmental protection of native species of Mexico of wild flora and fauna.
Price, W.W. 1899. Some winter birds of the lower Colorado Valley. Bulletin of the Cooper Ornithological Club 1:89–93.
Zamora-Arroyo, F., Pitt, J., Cornelius, S., Glenn, E., Hinojosa-Huerta, O., Moreno, M., Garcia, J., Nagler, P., de la Garza, M., Parra, I., 2005. Conservation Priorities in the Colorado River delta Mexico and the United States. Reporte preparado por Sonoran Institute, Environmental Defense, University of Arizona, Pronatura Noroeste Dirección de Conservación Sonora, CIAD y WWF, ISBN 968-817-726-1, 103 pp
Cover Photo: The headwaters of the Colorado River are in the Rocky Mountains (Colorado and Wyoming) and it flows more than 2,300 km down south into the Upper Gulf of California.
