MEXICO: THE ECOLOGY OF THE COLORADO RIVER

THE ENDANGERED SANTA CLARA WETLANDS
The lower Colorado River plays an important role in the migratory pathways of birds that winter in the southern United States and serves as the gateway for those species continuing south into Mexico. Although not extensively studied, the delta’s significance for migratory birds is indisputable, as it is the principal freshwater marsh in the region. A total of 358 bird species have been documented in the Colorado River Delta and upper Gulf of California region. From these, two are listed as endangered, six as threatened, and sixteen are under special protection in Mexico. Two wintering species and five breeding species have been locally extirpated, including the Southwestern Willow Flycatcher, the Fulvous-whistling Duck, and the Sandhill Crane.
birdcount
The delta supports a variety of wildlife, including several threatened and endangered species. Mexico’s Environmental Regulations on Endangered Species lists the following endangered species found in the delta:
• the Desert Pupfish, also listed as an endangered species in the U.S., the largest remaining population anywhere is in La Ciénega de Santa Clara
• the Yuma Clapper Rail, also listed as an endangered species in the U.S.
• the Bobcat
• the Vaquita porpoise, the world’s smallest marine cetacean, listed as a species of special concern by the U.S. Marine Mammal Commission. There are less than 250 vaquita left in the world.
• the Totoaba, now virtually extinct, a steel-blue fish that grows up to seven feet and 300 pounds and once supported a commercial fishery that died in 1975
• the Colorado Delta Clam, once an extremely abundant species and important in the ecosystem.

• The delta of the Colorado River is one of the major desert-river estuaries of the world and contains the largest wetland ecosystem in the Sonoran Desert.

Much of the delta has been converted into irrigated farmland; but approximately 250,000 hectares of unconverted delta land, too low for drainage and too saline for agriculture, still exists at the southern end of the delta in Mexico. Within this area lies the Cienega de Santa Clara, the largest brackish wetland habitat in the lower delta. This wetland is about to undergo major alteration in flow and salinity of input water due to activation of the Bureau of Reclamation’s Yuma Desalting Plant in Arizona.

• Prior to the construction of Hoover Dam and other upstream water diversions, the majority of the delta was lushly vegetated with an estimated 200 to 400 plant species I as well as numerous bird, fish, mammals. The Cienega de Santa Clara may be the largest wetland bird habitat left in the Delta long known for its higher concentrations of Yuma Clapper Rails and Pupfish than known elsewhere. Both species remain on the endangered list. Mexican officials have also expressed interest in cooperating to protect the delta wetlands where the diminished river trickles into the Gulf of California.

mouth of the Colorado River at entrance to the Gulf of California

The lower Colorado River also separates two great deserts, the Mojave on the California (western) side and the Sonoran on the Arizona (eastern) side. Over the eons the River has served as a genetic barrier, separating both sides as well as isolating species that can’t swim across the river or fly across the desert, limiting the development of subspecies in the region.

Birds of the Colorado http://www.pinesandprairieslandtrust.org/CRR_Bird_List.htm

Colorado River Nature Center http://www.azgfd.gov/outdoor_recreation/wildlife_area_co_river_nature.shtml