Sonny Bono Salton Sea National Wildlife Refuge Complex
Pacific Southwest Region
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Endangered and Threatened Species

With over 90 percent of California’s original wetlands gone, the Salton Sea has become one of the most important nesting sites and stopovers along the Pacific Flyway. In some years, as many as 95 percent of the North American population of eared grebes may use the Sea, 90 percent of American white pelicans, 50 percent of ruddy ducks and 40 percent of Yuma clapper rails. All of these species are of concern at either regional, continental or global scales. With its marine, freshwater, desert, wetland and agricultural habitats, the Sonny Bono Salton Sea National Wildlife Refuge provides habitat for hundreds of birds and wetland species, including several that have been listed as endangered or sensitive by the U.S. Fish and Wildlife Service.
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Endangered Species
Desert pupfish
Yuma clapper rail

California Bird Species of Special Concern
Burrowing owl
California brown pelican
Mountain plover

Birds of Interest
American white pelican
Black skimmer
Eared grebe
Peregrine falcon
Ruddy duck
Yellow-footed gull


Endangered Species

Desert pupfish (Cyprinodon macularius):
The desert pupfish was listed as endangered by the U.S. Fish and Wildlife Service on March 31, 1986. It is also listed as endangered by the State of Arizona. Desert pupfish are found in shallow water of desert springs, small streams, and marshes below 5,000 feet elevation. It tolerates high salt content and high water temperatures.
Pupfish.  (USFWS) It was once common in desert springs, marshes, backwaters, and tributaries of the Rio Sonoyta, lower Gila River, and lower Colorado River drainages in Arizona, California, and Mexico. Three natural populations of pupfish exist in Imperial and Riverside Counties, California. No naturally occurring populations remain in Arizona. Natural populations survive in four locations in the Colorado River delta, Sonora and Baja California, Mexico, and in the Rio Sonoyta in Sonora, Mexico. Introduced populations now exist in small springs, streams, and ponds in Imperial, Riverside, and Butte Counties, California, and in Pima, Pinal, Maricopa, Graham, Cochise, La Paz, and Yavapai Counties, Arizona.

Desert pupfish declined due to the introduction and spread of exotic predatory and competitive fishes, water impoundment and diversion, water pollution, groundwater pumping, stream channelization, and habitat modification. In the Salton Sea, desert pupfish are the only native fish species. They can be found in shoreline pools, agricultural drains, natural creeks and a few artificial refuge ponds. The actual use of the Sea itself by the desert pupfish is largely unknown. The protection and enhancement of existing habitats including shoreline pools, agricultural drains and natural creeks in the Salton Sea watershed are necessary for the future of this species in California.

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Yuma clapper rail (Rallus longirostris yumanensis):

The Salton Sea currently supports an estimated 40% of the entire U.S. population of this species. Due to the large percentage of this species using the habitats of the Salton Sea area, actions to preserve and increase fresh water marsh habitat may play a vital role in the recovery of the Yuma clapper rail. With decreasing water inflows to the Sea from water conservation and water transfers, marsh habitat for this species is expected to decYuma Clapper Rail.  (USFWS)rease.

The Yuma clapper rail was listed on the Endangered Species List on March 11, 1967. The disappearance of suitable habitat for this species has had the most direct impact on their declining numbers, although pollution has also contributed. Primarily, human-related modifications of wetland habitat, such as channelization, bank stabilization, and water impoundments have had the greatest impact. Furthermore, rail's prey upon crayfish, which are vulnerable to pesticides and heavy metal poisoning.

At the Sonny Bono Salton Sea National Wildlife Refuge, significant populations of Yuma clapper rails nest in the fresh water marshes maintained by the refuge. Water control projects on the Colorado River have built dams which altered the nature of this free-flowing body of water. Some backwaters were eliminated, but the dams created much new habitat for the birds by allowing sedimentation, which in turn allowed cattail and bulrush marshes to emerge. However, other suitable rail habitat has been lost through dredging and channelization projects along the Colorado River. In addition, the Salton Sea, while providing a significant amount of habitat, is becoming very salty. Regular outbreaks of botulism there have killed numerous birds, including rails.

Although the rail population appears stable, there is no denial that its fate is directly related to the various water projects along the Colorado River. It is clear that the key to preserving the Yuma clapper rail is the maintenance of early growth stages of cattail marsh by creating shallow water areas. The mats of dead cattails in the shallows will eventually provide nesting cover for the rails.

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California Bird Species of Special Concern

Burrowing owl (Athene cunicularia):
Burrowing owls were at one time fairly common and widespread over western North America. Populations have declined and in some cases have disappeared due to the large scale changes that humans have made to the owls habitat. They are listed as endangered or threatened in a number of states and are endangered in Canada. Burrowing owls are now federally listed as a Species of Management Concern and are a Species of Special Concern in California. The populations of burrowing owls in the Imperial Valley are year-round residents, unlike many populations that are migratory. The Imperial Valley also has the largest population of burrowing owls in the state of California - it is estimated that 70-80 percent of burrowing owls found in California reside in Imperial County.
Burrowing Owl.  (USFWS)
Burrowing owls nest in vacated burrows made by mammals such as ground squirrels or similar holes in the ground. Nest burrows are very distinctive because the owls line the entrance with material such as cow-manure, insect parts, cotton, dead toads, plastic and tin foil. Burrowing owls are diurnal, meaning they are active day and night. Most of them search for prey during the night. Prey items include mammals, birds, reptiles, amphibians, insects, spiders, centipedes, scorpions, crayfish, and mollusks.

In the Imperial Valley burrowing owls can most often be seen along irrigation drains, canals, and delivery ditches. The Imperial Irrigation District searches for owl burrows before any concrete canal lining projects are started. If owls are found nesting within an area that may be affected by such a project, construction is delayed until the young have left the burrow. There is currently a statewide census of burrowing owls that has helped to determine if owl populations are reaching an endangered status. The census studied owl breeding patterns and provided critical information for plans to protect them.

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California brown pelican (Pelecanus occidentalis):
California Brown Pelican.  (USFWS)
The Salton Sea currently supports a year round population of California brown pelicans. Peak numbers can reach 5,000 individuals. This species nested successfully at the Salton Sea (first nesting of a CA brown pelican on an inland lake) in 1996 and has attempted nesting since then. Mexican and United States biologists feel the Salton Sea may prove to be important in the recovery of this endangered species and has proven to be important to the Sea of Cortez population for range expansion. Ensuring open water (fresh and salt), a food resource and islands for roosting and nesting are critical for this species.

The California brown pelican was listed on the Endangered Species List on June 2, 1970. The primary reason for its decline was the use of DDT and polychlorinated biphenyls, which resulted in thin-shelled eggs that were easily broken during incubation or another impairment of reproductive success. The Environmental Protection Agency banned the use of DDT in 1972 and has also restricted use of edrin, a type of polychlorinated biphenyl related to brown pelican declines. Since that time the nesting success has risen as the levels of these compounds have decreased in most areas.

California brown pelicans at the Salton Sea are sometimes afflicted with botulism, which is caused by eating fish that also carry the disease. Botulism paralyzes the muscles of diseased birds, which is eventually fatal. U.S. Fish and Wildlife staff at the Sonny Bono Salton Sea National Wildlife Refuge conduct air boat surveys of the Sea during botulism outbreaks, collecting dead and sick birds. Pelicans in the early stages of botulism are sent to rehabilitation centers, where they are cared for and later released. For more information, see our wildlife disease page.

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Mountain plover (Charadrius montanus):
In 1999, the mountain plover was proposed as a threatened species on the Endangered Species List. This means that the Fish and Wildlife Service, after thoroughly examining the best scientific information available, believes that the mountain plover is likely to become endangered in the foreseeable future throughout all or a significant potion of its range unless actions are taken now to reverse the decline in population. The mountain plover is important because it, and other native species, are indicators of the health of native prairies. The decline of the mountain plover is an early warning that the replacement of many native grasslands with urban development or grazing and farming practices, are hindering the survival of the short-grass prairie.

The decline in the mountain plover population is due to a combination of factors - native grasslands being replaced by agriculture and urban development; early spring plowing and planting on dryland nesting sites; and loss of prairies dogs and other burrowing rodents. Mountain plovers are commonly found attempting to breed on plowed land in several states, however surveys have found that successful nesting is interrupted by subsequent planting and crop growing before nesting is complete. In addition, livestock grazing practices that encourage taller grasses and forbs eliminate mountain plover habitat.

The Imperial Valley has one of the largest wintering populations of this species in the Pacific Flyway with 1,000 to 1,500 typically in the Valley. The species is migratory, spending winters in the south-western U.S. and Mexico and summer at their breeding grounds further north in suitable short-grass prairie habitat. Mountain plovers are gregarious during the winter, and can be seen in grassy or bare soil fields.

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Birds of Interest


American White Pelican.  (USFWS)

American white pelican (Pelecanus erythrorhynchos):
This species is both migratory and resident at the Salton Sea. Peak numbers of white pelicans using the Sea have been recently estimated at 26,000 during spring migration. This is thought to comprise between 80 and 90% of the entire Western population of American white pelicans. The Salton Sea provides a vital link in the migratory path of this species on the Pacific Flyway. The longest migratory jump for white pelicans on the flyway is between the Salton Sea and the Central Valley. Without the resources of the Salton Sea, white pelicans would be forced to fly even further to rest and forage during migration.

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Black skimmer (Rynchops niger):
Black skimmers are common at the Salton Sea during the breeding season (in the summer months), and several hundred nesting pairs have been recorded in previous years, representing the largest population of black skimmers in Western North America. Black skimmers are unique in that their bill (consisting of an upper and lower mandible) is unlike anyBlack Skimmer.  (USFWS) other bird. The lower mandible is longer than the upper mandible. This is an adaptation to the feeding method used by the black skimmer: while foraging, they fly with their lower mandible slicing through the water, catching crustaceans and other prey items. The lower mandible would be quickly eroded away by friction if it did not grow roughly twice as fast as the upper mandible. Skimmers in zoos, deprived of the opportunity to skim, soon have lower mandibles much, much longer than the upper.

Black skimmers winter in South America, as far south as southern Chile and central Argentina. Millinery trade in the past targeted skimmers for their feathers, which were used in hat decorations, and eggs were also taken by humans. Even slight human disturbance at a nesting colony can reduce the reproductive success.

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Eared grebe (Podiceps nigricollis):
The Salton Sea is the wintering destination and migratory stop over for up to 1 million eared grebes, approximately 95% of the continental population for this species. This species typically migrates through Mono Lake and Salt Lake to the Salton Sea and seems to prefer the saline lake environments. Without the Salton Sea, eared grebes normally wintering at the Sea would be forced to migrate to the Sea of Cortez.

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Peregrine falcon (Falco peregrinus):
Peregrine falcons were at one time common in parts of the Appalachian Mountains and nearby valleys from New England south to Georgia, the upper Mississippi River Valley, and the Rocky Mountains. They also inhabited mountain ranges and islands along the Pacific Coast from Mexico north to Alaska and in the Arctic tundra. Beginning in the late 1940s, peregrine falcons suffered a devastating and rapid decline. By the mid-1960s, the species had been eliminated from nearly all of the eastern U.S. Although less severe, the decline spread west, where peregrine populations were reduced by 80 to 90 percent by the mid-1970s.

The cause of the decline in the population was due to unusually high concentrations of the pesticide DDT and its breakdown product DDE in peregrine falcons and other birds of prey. The peregrine accumulated DDT in their tissues by feeding on birds that had eaten DDT-contaminated insects or seeds. The toxic chemical interfered with eggshell formation. As a result, falcons laid eggs with shells so thin they often broke during incubation or otherwise failed to hatch. Because too few young were raised to replace adults that died, peregrine populations declined precipitously. The falcon was listed as endangered in 1970. In 1972 the EPA banned DDT for most uses in the U.S. The reduction in DDT use as well as the reintroduction of peregrine falcons throughout the U.S. has helped the population rebound. Populations are now estimated at 1,650 breeding pairs in the U.S. and Canada, with additional birds in Mexico. In August 1999, the U.S. Fish and Wildlife Service removed the peregrine falcon from the list of endangered and threatened species, marking one of the most dramatic successes of the Endangered Species Act.

At the Salton Sea, peregrines can be seen frequently. Several pairs have nested at the Sonny Bono Salton Sea National Wildlife Refuge. The future of the species is still dependent on the continued ban of DDT and other similar pesticides.

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Ruddy ducks (Oxyura jamaicensis):
The Salton Sea provides wintering habitat for an estimated 50% of the total number of ruddy ducks found in the Pacific Flyway. Future wetland loss and habitat degradation may increase the importance of the Salton Sea to this species. Protecting open water habitat and food resources are important to maintaining this species at the Salton Sea.

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Gull.  (USFWS)

Yellow-footed gull (Larus livens):
The yellow-footed gull is a fairly common visitor to the Salton Sea - which is one of the only places in the United States that this species can be seen. The gulls breed in the Gulf of California, and can be seen after this period at the Salton Sea. A few usually linger at the Sea into winter, and they are very rare in spring. They can also be found occasionally on the coast of southern California.

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The Salton Sea has been designated as an internationally important staging area for shorebirds. Over 124,000 shorebirds of at least 25 species migrate through the Salton Sea along the Pacific Flyway. It is considered the third most important shorebird habitat west of the Rocky Mountains. Several species rely heavily on the Salton American Avocets (upper left), Black-necked Stilt (lower right).  (USFWS)Sea to support a large portion of their flyway population including:
1. Western sandpipers (Calidris mauri) (54,000)
2. American avocet (Recurvirostra americana) (19,000)
3. Dowitcher spp. (Limnodromus spp.) (12,000)
4. Red-necked phalarope (Phalaropus lobatus) (12,000)
5. Whimbrel (Numenius phaeopus) (9,800)
6. Black-necked stilt (Himantopus mexicanus) (10,000)

In addition the Salton Sea supports the greatest number of Western snowy plovers in the interior of California. Coastal populations of this species are listed as Federally Threatened. The Salton Sea could play an important role in the future for snowy plover populations.

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Last updated: May 23, 2011