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Sections dealing with birds, excerpted from the

Final Environmental Impact Report
for Modified East Lowline and Trifolium Interceptors, and Completion Projects, Volume 1. Imperial Irrigation District,
May 1994

 

Chapter 3: Environmental Setting

Section: 3.4.3 Special Status Wildlife - Birds

Section: 3.4.4 Aquatic birds in the Imperial Valley

BIRDS

The Salton Sea and Imperial Valley provide habitat for numerous special-status bird species. Table 3.4-4 summarizes the special-status species identified by the USFWS and CDFG. Special-status species include listed, proposed, and candidate spe-cies under consideration for listing. The Salton Sea National Wildlife Refuge (NWR) has records of many special-status species occurring in the refuge, around the sea, and in adjacent Imperial Valley. Only a portion of these observations has been entered in the Natural Diversity Data Base. Most of the special-status birds are rare in the Impe-rial Valley, but may occur as occasional visitors or regular migrants. A brief discussion of each sensitive avian species and its known or expected occurrence in the Imperial Valley or project areas is presented below. Habitat and occurrence information is largely from CDFG (1990). Population data and foraging habitat are from Setmire et al., 1993.

Brown Pelicans. The California brown pelican probably had little historical use of the Salton Sea, although the Rio Colorado Delta habitats of the past were probably always important feeding areas (Anderson, 1993). The nearest brown pelican breeding colon-ies are located in the Gulf of California on San Luis Island (about 220 miles southeast; breeding populations vary between 4,000 and 12,000 pairs), Puerto Refugio area (1,000 to 4,000 breeding pairs), and Salsipuedes/Animas/San Lorenzo area (breeding populations vary between 3,000 to 18,000 pairs) (USFWS, 1983). Even today, post-breeding brown pelican populations occupy and utilize coastal habitats in the northern Gulf of Californis (Rio Colorado Delta area) for roosting and feeding. It is not uncommon to encounter 30,000 to 40,000 individual brown pelicans in the northern Gulf of Californis (D.W. Anderson, personal observations during aerial surveys in post studies). Overall, the Salton Sea seems to provide better habitat conditons for brown pelicans than other inland locations in the regions, but the number of brown pelicans at the sea represents less than 1 percent of the species' population. Most of the birds use typical estuarine and marine habitats of the Gulf of California and Pacific Coast.

3.4-15

 

Table 3.4-4
Special-Status Bird Species in the Imperial Valley Area

Sheet l of 2

Species
Status
Local Habitat

Pelecanus occidentalis californicus
California brown pelican

USFWS: Endangered
CDFG: Endangered

Open water of the Salton Sea

Pelecanus erythroryhnchos
American white pelican

CDFG: CSC

Open water of the Salton Sea

Phalacrocorax auritus
Double-crested cormorant

CDFG: CSC

Open water of the Salton Sea and rivers

Ixobrychus elixisb
Least bittern

USFWS: Candidate C2
CDFG: CSC

Freshwater marsh and open water of the Salton Sea

Plegadis chihib
White-faced ibis

USFWS: Candidate C2
CDFG: CSC

Freshwater marsh/agricultural

Mycteria americana
Wood stork

CDFG: CSC

Freshwater rnarsh/Salton Sea mudflat

Branta canadensis leucopareia
Aleutian Canada goose

USFWS: Threatened

Agricultural/freshwater marshes

Dendrocygna bicolorb
Fulvous whistling duck

USFWS: Candidate C2
CDFG: CSC

Freshwater marshes

Pandion haliaetus
Osprey

CDFG: CSC

Open water of the Salton Sea

Haliaeetus leucocephalus
Bald eagle

USFWS: Endangered
CDFG: Endangered

Open water of the Salton Sea/agricultural

Circus cyaneusb
Northern harrier

CDFG: CSC

Agricultural/freshwater marsh

Accipiter striatusb
Sharp-shinned hawk

CDFG: CSC

Riparian/shrubland

Buteo regalis
Ferruginous hawk

CDFG: CSC

Agricultural fields

Accipiter cooperii
Cooper's hawk

CDFG: CSC

Riparian/shrubland

Falco perigrinus anaturn
American peregrine falcon

USFWS: Endangered
CDFG: Endangered

Open water of the Salton Sea/freshwater marsh

Falco mexicanus
Prairie falcon

CDFG: CSC

Open water of the Salton Sea/freshwater marsh

Laterallus jamaicensis coturniculusb
California black rail

CDFG: Threatened

Marshes

Rallus longirostris yumanensisb
Yuma clapper rail

USFWS: Endangered
CDFG: Threatened

Marshes

Grus canadensis tabida
Greater sandhill crane

CDFG: Threatened

Agricultural

Charadrius alexandrinus nivosusb
western snowy plover

USFWS: Threatened
CDFG: CSC

Salton Sea mudflat

Charadrius motanus
Mountain plover

USFWS: Candidate C2
CDFG: CSC

Agriculture

Numenius americanus
Long-billed curlew

USFWS: Proposed (Endangered)
CDFG: CSC

Freshwater marsh/agricultural

Sterna antillarum browni
California least tern

USFWS: Endangered
CDFG: Endangered

Shorelines of open waters

Chliodonias niger
Black tern

USFWS: Candidate C2
CDFG: CSC

Salton Sea mudflat/agricuitural

3.4-16

Table3.4.4

Special-Status Bird Species in the Imperial Valley Area

Sheet 2 of 2

Species
Statusa
Local Habitat

Sterna niloticab
Gull-billed tern

CDFG: CSC

Salton Sea mudflat/agricultural

Rynchops nigerb
Black skimmer

CDFG: CSC

Open water/mudflats of theSalton Sea

Athena cuniculariab
Burrowing owl

CDFG: CSC

Small mammal burrows alongdrains and canals/agricultural

Lanius ludovicianus
Loggerhead shrike

USFWS: Candidate C2
CDFG: CSC

Desert riparian/agricultural

Polioptila melanura
Black-tailed gnatcatcher

CDFG: CSC

Desert wash and riparian

Vireo bellii arizonae
Arizona Bell's vireo

CDFG: Endangered

Desert riparian

Passerculus sandwichensis rostratus
Large-billed savannah sparrow

USFWS: Candidate C2
CDFG: CSC

Desert riparian Malt cedar scrub

Amphispiza bellii bellii
Bell's sage sparrow

USFWS: Candidate C2
CDFG: CSC

Desert scrub and alkali desert scrub

aSource: USEWS, 1991

CDFG, 1994
CDFG, 1992d

bSpecies known to breed in area

Federal Candidate Species Designations

Cl = Enough data are on file to support the federal listing

C2 = Threat and/or distribution data are insufficient to support federal listing

C3c = Too widespread and/or not threatened

State Candidate Species Designations

CCE = California Candidate Endangered

CSC = California Special Concern

CFP = California Fully Protected

3.4-17

In 1977, Anderson et al. (1977) became interested in the passive dispersal of brown pelicans into the southwestern desert area, due to storm patterns (Anderson, 1993). At that time, they concluded that this phenomenon did not result in significant population losses, and the losses were not important to population maintenance, but that inland occurrences were of interest as a case study of potential range-expansion phenomena in birds. Anderson et al. (1977) speculated that populations of brown pelicans, like other species from the Gulf of California, might become established migrants and regular users of this "new" habitat if a tradition developed. There were no signs of any tradition in 1977, and several criteria would be necessary to test the idea of a tradition of use: (1) increasing numbers arriving at regular times, (2) evidence that the Salton Sea could indeed support numbers of brown pelicans over long periods of time (such as overwintering individuals), and (3) indications (from age-ratios) that older age-class birds were using the Salton Sea. None of these indications existed in the late 1970's.

Anderson (1993) reviewed the journal American Birds for indications that brown pelicans have become regular and traditional users of the Salton se. Brown pelican use of the Salton Sea has certainly increased in recent years (Figure 3.4-3). It is possible that, initially, this increased use of the Salton Sea was particularly enhanced by the flooding of the lower Colorado Delta area (which enhanced dispersal) in the late 1970s and early 1980s (it has since dried up) (D.W. Anderson, personal observations). Although there were indications of overwintering brown pelicans at Salton Sea in the mid-1980s (Table 1 in Anderson, 1993), the first confirmed overwintering was in the winter of 1987 (McCaskie, 1987).

In April and May of 1992, McCaskie (1992a) reported more than 400 brown pelicans at Salton Sea, none of which were juveniles. This agrees with D.W. Anderson's own studies in the Gulf of California at that time (Anderson, 1993). The breeding season of 1992 was during an El Niño year. These are years when water temperature interactions result in poor or no breeding in the Gulf of California. There were no young available to disperse into the Salton Sea in May of 1992, but later (June 1992), McCaskie (1992b) reported that a few young-of-the-year were present at Salton Sea. By June, the only colony to produce significant numbers of yound in 1992, San Luis Island (some 10,000 young were produced that year), was fledging new yound and they were leaving the nesting colony at that time. Other than these newly fledged young, the sources of Salton Sea brown pelicans in 1992 could have been any breeding colony in the Gulf of California. D.W. Anderson received no reports of marked or banded pelicans from any of the many birdwatchers who frequent the Salton sea, although his earlier band-recovery data indicated multiple sources for inland dispersing brown peli-cans (Anderson et al., 1977).

3.4-18

Figure 3.4-3: Maximum Number of Brown Pelicans Observed on the Salton Sea from the 1950's through 1992
Sources:Anderson et al. (1977) and McCaskie (various years; see text)

3.4-19

About 5 percent of adults in Salton Sea brown pelican flocks are now reported as "typi-cal" (other than situations similar to the above, where occasionally incoming flocks might be almost entirely birds older than 1 year) (Anderson, 1993). Adults also now typically arrive later than the mostly newly fledged young each year. Without specific expertise, there could be some problems in separating newly fledged young-of-the-year (known as YY or HY) from 1-year-old brown pelicans (D.W. Anderson calls them "DWs") (see Schreiber et al., 1989). Therefore, even flocks of pelicans including many 'juveniles" as reported in American Birds could include DWs and therefore individuals with a previous year's experience at the Salton Sea. People who work in the area now consider 1,000 to 2,000 post-breeding brown pelicans as "regular" at Salton Sea. Setmire et al. (1993) gives the number of individuals as 5,000, indicating a large amount of uncertainty in the actual numbers. Overwintering by small numbers (per-haps less than 10 to 15) of brown pelicans is also regular now at the Salton Sea. Although lacking proof-positive (radio-telemetry data on known individuals), Anderson (1993) concludes brown pelicans do not breed at the Salton Sea, but this species (numbers ranging from 1,000 to 5,000) has become a regular, expected migrant to the Salton Sea.

Both brown and white pelicans will feed on any fish species that occurs near the sur-face, and concentrated and/or stressed/vulnerable fish in anoxic or very shallow water or other unusual conditions will become especially vulnerable and "useful" to either of these two species (Anderson, 1993). The major differences in foods between the two species will usually be in size: the white pelican can consume fish considerably larger than those taken by brown pelicans (4 to 5-pound fish versus 1- to 2-pound fish and smaller), although both species frequently take smaller fish. Feeding primarily at the Salton Sea, the two pelican species often feed together, and greatest numbers occur around the mouths of the Alamo and Whitewater Rivers (McKernan, 1993).

White Pelicans. The American white pelican has probably always migrated through the lower Colorado River Delta area, regardless of its past configuration (Anderson, 1993). Today, the importance of the Salton Sea area (Jehl et al., 1977) is probably related to ecological changes and habitat improvement since the early 1900s, when the Salton Sea was re-created by accident. As a breeding species, the white pelican even colonized the Salton Sea in the decade following its creation (Grinnel, 1908). White pelican nesting has not been known at the Salton Sea, however, since at least the 1930s. Adequate, undisturbed habitat probably no longer exists for nesting to be possible for white pelicans at the Salton Sea (Anderson, 1993).

In winter, however, the Salton Sea has remained the site of major white pelican con-centrations from populations that breed in the north (Johnsgard; 1993). In radio-telem-etry studies during 1991, individual pelicans migrating south from northern California (Clear Lake National Wildlife Refuge, where breeding populations have fared quite poorly over the past decade) were documented as using the Salton Sea (Anderson, 1993). The high populations of white pelicans at the Salton Sea in the early- to mid-1980s (Table 1 in Anderson, 1993; Figure 3.4-4)were likely associated initially with extensive flooding in the lower Colorado Delta area from the late 1970s through the mid-1980s, when many white pelicans came to reside in the region for a substantial portion of the wintering period, using Salton Sea/Laguna Salada Rio Hardy wetlands as wintering habitat (previous discussions citing surveys by R. McKernan, and t).W. Anderson's personal observations at the time, while working on other projects in the area).

3.4-20

Most recent censuses of Salton Sea white pelicans by J. MacKay (Anderson, 1993) indicate that use may be declining in recent years, but that the area still supports perhaps several thousand white pelicans for significant periods of winter (Figure 3.4-4; Anderson, 1993; Setmire et al., 1993). Although accurate data are not available to compare relative numbers of white pelicans at the Salton Sea with those found at other typical habitats in the region (such as wildlife refuges along the lower Colorado River and the Gulf of California), the population at the sea is probably much larger than at the other areas (Anderson, 1993).

White pelican populations in the western part of North America have declined over the past 4 to 5 decades, due in part to habitat changes created by water development proj-ects, human disturbance of nesting colonies, and effects of pesticides (Boelstorff et al., 1988; Anderson, 1993). These long-term population changes have recently been coupled with further exacerbations from a 7-year drought that ended in 1992.

USEWS data (USFWS, 1993a) also indicate smaller numbers of white pelicans have used Salton Sea (and adjacent wetlands) than the most recent peak numbers in 1985. Overall, the USFWS counts in combination with data summarized above indicate that 2,000 to 17,000 white pelicans have used the Salton Sea as over-wintering habitat over a period up to about 6 months. The number given by Setmire et al. (1993) is 5,000 white pelicans.

Double-Crested Cormorant. Double-crested cormorants, a California Species of Special Concern, are residents of the Salton Sea area. Pesticides exposure, predation of eggs and young by crows and gulls, habitat losses, and human disturbance are factors respon-sible for their recent declining populations (CDFG, 1990). The Salton Sea cormorant population is estimated at approximately 10,000 birds. Small numbers (approximately 57-63 nests in 1987-1988) of cormorants nested at the Salton Sea, however, no nesting has been reported since 1989 (USFWS, 1993a). Exposed rocks, islands, and dead tree branches are used as roosts; undisturbed sites near water are required for nesting. Cormorants regularly move between the Salton Sea and the lakes at the Finney-Ramer Unit of the Imperial Wildlife Management Area, feeding primarily on fish that they catch by diving under water. Occasional foraging will also occur in open water along the New and Alamo Rivers.

Least Bittern. The least bittern is a federal Candidate C2 and California Species of Special Concern. Marsh drainage, pesticides, and human disturbance have contributed to the decline in bittern populations. Least bitterns are residents of the Salton Sea and Colorado River wetlands, although additional individuals migrate to the area in summer. The least bittern population is estimated to be about 550 birds. Bitterns feed mainly on small fish, crayfish, insects, and occasionally on amphibians and small mammals. Roosting occurs in dense salt cedar stands; nests are built in dense emergent vegetation. Foraging occurs in freshwater marshes and Salton Sea beach or mudflats.

3.4-21

Figure 3.4-4: Maximum Counts (Usually Occurring in February) of American White Pelicans at Salton Sea
Sources:J. MacKay, USFWS, pers comm. National Wildlife Refuge During 1984 to 1990

3.4-22

White-Faced ibis. The white-faced ibis is a California Species of Special Cdhcern afid a federal Category 2 species. Loss of habitat and pesticide contamination have contri-buted to the decline in numbers. This species no longer breeds regularly within Califor-nia and is rare in the Salton Sea area. Ibises are associated with fresh emergent wet-lands and flooded pastures, meadows, and crops. Forage includes small fish, amphibi-ans, a variety of invertebrates, and grain. Ibises are uncommon at the Salton Sea from April to September but common during fall and winter. Population estimates vary greatly, and numbers up to 20,000 have been reported. Ibises regularly occur at the Salton Sea NWR, and large flocks of 4,000 ibises may forage on agricultural fields and wetlands in the northern portion of the Imperial Valley.

Wood Stork. The wood stork is a California Species of Special Concern. Small num-bers (about 275 birds) of wood storks are regularly found in the Imperial Valley during post breeding migration. Historically, large numbers of wood storks occurred in Florida, but loss of breeding and foraging habitat led to declines in the 1930s. Large numbers (4,000 birds) of wood storks were reported in the Imperial Valley in the 1950s, but numbers in recent years have been low. Breeding occurs in florida only. Wood storks visit the Imperial Valley in midsummer, usually in July, to forage in marsh areas. Food items include small fish, aquatic invertebrates, and amphibians.

Fulvous Whistling-Duck. The fulvous whistling-duck is a state Species of Special Con-cern and a federal Category 2 species. Loss of habitat and destruction of nests are viewed as causes of the species' decline. The whistling-duck is associated with fresh emergent wetlands, lacustrine, and riverine habitats. Salton Sea area populations are estimated at about 200 birds. This duck rarely nests in the Imperial Valley in dense wetlands near the Salton Sea. Nests are typically constructed on high ground in dense cattails near the southern end of Salton Sea. Feeding on wetland plants and sub-merged aquatic vegetation occurs at night. This duck is a common resident in the Imperial Valley.

Aleutian Canada Goose. The Aleutian Canada goose is listed as a federal Threatened species. It breeds on the Aleutian Islands in Alaska, but winters primarily in California and Oregon (Ehrlich et al., 1992). Large numbers of Aleutian Canada geese winter throughout the Central Valley, Imperial Valley, and northeastern California. Numbers reported for the Imperial Valley area range up to 5,000 birds. Preferred foraging habi-tats of these geese include lacustrine, fresh emergent wetlands, and moist grasslands, croplands, pastures, and meadows (CDFG, 1990). Geese feed on a wide variety of marsh vegetation: algae, seeds of grasses and sedges, grain (especially in winter), and bemes. Predation by Arctic foxes on their summer range, hunting, and loss of winter-ing habitat are primarily responsible for reduced numbers of the Aleutian Canada geese (Ehrlich et al., 1992).

Osprey. Ospreys are a California Species of Special Concern and are rare visitors (typi-cally five birds) to the Imperial Valley. Ospreys prey almost entirely on fish they catch near the surface of open waters at the Salton Sea. Breeding occurs only in northern California and northward where ospreys build nest platforms of-sticks on trees, cliffs, or artificial structures close to water. Ospreys compete with bald eagles and gulls for food.

3.4-23

Bald Eagle. The bald eagle is listed as federal Endangered, California Endangered, and California Fully Protected. Bald eagles are predators that forage mostly on fish; how-ever, they are opportunistic and will take birds, mammals, and carrion. Historically, declines in bald eagle populations result from uncontrolled shooting by humans, con-tamination of prey by pesticides, and loss of critical habitat. Human disturbance and habitat loss continue to threaten eagles. Foraging in the Imperial Valley occurs in open water of the Salton Sea and agricultural fields. A few winter migrants (one to three birds) have been regularly observed at the Salton Sea, but are rarely observed during the fall. Bald eagle populations and distribution are increasing in California in the Sierra Nevada range and at some lakes and reservoirs in the Coast Ranges, but resi-dent and breeding populations of bald eagles are still rare in the rest of California.

Northern Harrier. The northern harrier is a state Species of Special Concern. Northern harriers feed mostly on voles but also eat other small mammals, birds, frogs, reptiles, crustaceans, and insects. Harriers usually nest on the ground in shrubby vegetation in emergent wetland, along rivers or lakes, in grasslands, or on sagebrush flats.

Sharp-Shinned Hawk. This Species of Special Concern prefers dense, even-aged, single-layered forest canopies for nesting. Their current breeding status is not well docu-mented in California. Approximately 250 winter migrants occur in the Imperial Valley. Sharp-shinned hawks feed mostly on small birds and will also prey on small mammals, reptiles, amphibians, and insects. These uncommon hawks will forage along riparian shrubland areas.

Cooper's Hawk. The cooper's hawk is a Species of Special Concern whose breeding numbers have declined. These hawks are residents throughout most of California and are usually associated with wooded areas, often nesting in stands of deciduous trees near riparian areas. Approximately 300 migrants occur in the Imperial Valley. Forag-ing habitat occurs near tree stands of riparian corridors and shrubland. The species preys mostly on small birds, occasionally small mammals and reptiles.

Ferruginous Hawk. Ferruginous hawks are a Species of Special Concern and a federal Candidate 2 for listing. They winter in California in open habitats such as grassland and semiarid brushlands where they feed on small mammals (especially rabbits and woodrats), amphipods, reptiles, and invertebrates. This species is mainly observed foraging in agricultural fields in the Imperial Valley; therefore, individuals could occur over the project area as fall and winter migrants pass through the area.

American Peregrine Falcon. The peregrine falcon has been a federal and state listed Endangered species for many years because of drastic losses from failure of eggs to hatch due to DDT residues. Peregrmnes range throughout California during migration and are now nesting in most areas of the state, except desert regions. Numbers have been increasing in recent years because of captive breeding programs established under the Pacific Coast Recovery Plan (USFWS, 1982). Since 1977, 657 peregrmnes have been released throughout California to augment natural breeding success (CDFG, 1992d). The statewide breeding population is stable or increasing in most areas, although some areas have low numbers.

3.4-24

Small numbers of migrant peregrines (one to three buds) have been regularly observed over Salton Sea marsh areas, particularly the Salton Sea NWR, which attracts many waterfowl and other birds. No nesting sites are known or expected in the Imperial Valley area. Nesting sites are typically found on ledges of cliffs, often near water. These falcons prey on other birds in flight and often hunt over wetlands, farm fields, woodlands, and other habitats. Peregrine falcons feed mostly on shore birds up to duck size but will occasionally take mammals, insects, or fish.

Prairie Falcon. The prairie falcon is a Species of Special Concern in California. Prairie falcons generally nest on a sheltered cliff ledge overlooking an open area. They may also nest on an old eagle or raven stick nest on a cliff or bluff. Approximately 30 migrants occur in the Imperial Valley. They eat mostly small mammals and some small birds and reptiles. Falcons will forage over open water of the Salton Sea and freshwater marshes.

Yuma Clapper Rail. The Yuma clapper rail is a state Threatened and federally Endan-gered species generally found in the Salton Sea area from April to September. Loss of habitat has caused a decline in rail populations. Populations are known from sites along the south shore of the Salton Sea in the vicinity of the New and Alamo River deltas and in areas protected by the Salton Sea NWR (CDFG, 1979, 1990, 1992c; USFWS, 1993b) (Table 3.4-5). Sightings reported to the CNDDB are listed in Table 3.4-5 and shown in Figure 3.4-5.

Since 1984, annual rail surveys have been conducted on or adjacent to the Salton Sea NWR by USFWS staff (see Table 3.4-5). Rail numbers, both individuals and pairs, have been fairly static over the period from 1984 to 1991 with 1 to 8 pairs and 5 to 25 individuals being recorded (USEWS, 1993a). In 1992 and 1993, numbers of rails detected had noticeably increased (15 to 27 pairs and 40 to 60 individuals). The number of rail pairs (15) detected in 1992 was almost 300 percent above the 8-year average from 1984 through 1991. Displacement by higher Salton Sea water levels, flooding on the Gila and lower Colorado River, and habitat management improvements were possible factors in this increase (USFWS, 1993a). However, other areas not sub-ject to flooding or habitat management also had more rails than previous years. The USFWS surveys cover many areas near the Salton Sea. Additional rail populations occur at Wister Wildlife Area where 310 birds were counted in 1993. Rails also have been detected at Holtville Main Canal, Salt Creek, Whitewater River, Mammouth Wash, other Salton Sea shoreline areas, and private lands. This rail is associated with freshwater and saline emergent wetlands. Food items include crabs, clams, mussels, snails, insects, spiders, and worms. Nests are built in thick stands of cordgrass, cattails, or bulrushes. It appears that dispersing rails may forage or potentially breed through-out the Imperial Valley wherever suitable marsh habitat occurs.

3.4-25

Table 3.4-5
Occurrences of Special-Status Birds In the Project Vicinity
Common Name
Location Sighted
Habitat
Number of Individuals

Year Sighted

Yuma clapper rail

New River (NNW Seeley) (12)

River
2 or mort (not specific)
--

Yuma clapper rail

Alamo River(Near Ramey and Finney)(13)

River
5
1982a

Yuma clapper rail

SSNWR (New River) (14)

Marsh
49
1978a

Yuma clapper rail

SSNWR (Rock Hill) (15)

Marsh
2
1978a

Yuma clapper rail

SSNWR (All Areas)

Marsh
10
1984c

Yuma clapper rail

SSNVTR (All Areas)

Marsh
21
1985e

Yuma clapper rail

SSNWR (All Areas)

Marsh
25
1986e

Yuma dapper rail

SSNWR (All Areas)

Marsh
20
1987e

Yuma clapper rail

SSNWR (All Areas)

Marsh
18
l988e

Yuma clapper rail

SSNWR (All Areas)

Marsh
5
1989e

Yuma clapper rail

SSNWR (All Areas)

Marsh
16
1990e

Yuma clapper rail

SSNWR (All Areas)

Marsh
13
1991e

Yuma clapper rail

SSNWR (All Areas)

Marsh
40
1992e

Yuma clapper rail

Wister WMA (16)

Cattail/Bulrush Marsh
3l/86
1985/1989a

Yuma clapper rail

Wister WMA (16)

Marsh
310
1992e

Yurna clapper rail

Holtville Main Drain (17)

?
4 (not specific)
1987a,f

Yuma clapper rail

NW of Weatmorland (18)

River-Gravel beach/Salt Cedar
3

1975a,f

Black rail

Coachella Canal (1)

Marsh
2

1975a,ff

Black rail

Haley Rd. (2)

?
1

1975a,f

Black rail

Montgomery Rd. (3)

Marsh
1

1975a,f

Black rail

Siphon #4 (4)

Marsh
5

1975a,f

Black rail

Siphon #5 (5)

Marsh
2

1975a,f

Black rail

Calipatria (6)

Orchard Seep
1

1989b

Black rail

Coachella Canal (7)

Unlined Canal Marshes
14

1989b

Black rail

All American Canal (8)

Unlined Canal Marshes
11

1988c

Black rail

New River (10)

Drain Marsh
13

1989b,d

Black rail

Finney Lake (11)

Marsh
1

1989b

Black skimmer

Mullet Island (19)

Alkali Mudflat
2 (nest with egg)

1973a

aCDFG, 1992b
bEvens et al, 1991
cJackson 1988
dLaymon, et al., 1990
CUSFWS 1993b
fHabitat which was supported by the unlined Coachella Canal has desiccated due to the completion of a concrete-lined canal parallel to the earthen Coachella Canal in 1981.

Notes: Location numbers refer to Figure 3.4-5.

3.4-26

Figure 3.4-5: Approximate Locations of Special-Status Species
(Source: CDFG, 1992b; Evens et al., 1991)

3.4-27

 California Black Rail. Black rails are a federal Category 1 species, listed by California as Threatened and Fully Protected. The reduced population of this species is attri-buted to loss of wetland habitat in many areas of the state. Black rails are found in saline, brackish, and freshwater emergent wetland habitats in several areas in Califor-ma, including the Imperial Valley and the lower Colorado River. Nesting occurs in dense stands of bulrushes, cattails, or saltgrass. Sightings of black rails reported to the CNDDB are given in Table 3.4-5 and shown in Figure 3.4-5. Black rails are residents of the Imperial Valley, but their secretive habits limit observations.

Studies of black rail distribution have identified several locations in or adjacent to the Imperial Valley with black rail populations (Jurek, 1975; Jackson, 1988; USBR, 1993; Evens et al., 1991). Historic records of rails in the Salton Trough identified marsh areas with rails as near the Salton Sea, Finney Lake, and in seepage areas adjacent to the All-American Canal and the Coachella Canal (Evens et al., 1991). In 1974, eight marshes with rails were identified in the area south of Niland along the Coachella Canal (Jurek, 1975). The Coachella Canal south of Niland was concrete-lined in 1981, and all black rail habitat supported by canal seepage has desiccated (Evens et al., 1991). Surveys of marshes supported by seepage from unlined portions of the Coachella Canal by Jackson in 1988 and again by Evens et al. in 1989 detected rails at eight sites. These marsh areas are north of Niland and outside of the proposed project areas. Additional surveys for black rails were conducted in 1989 in the Salt Creek marshes by the Bureau of Reclamation (USBR, 1993).

Rail surveys have not been conducted on the East Highline Canal (Jackson, 1993; Evens, 1993). During field surveys, marsh habitat was observed at two locations along the East Highline Canal where seepage supports small marshes with standing surface water. A small (<0.25-acre) marsh consisting of open water and scattered emergent vegetation occurs on the east side of the canal near the Standard Lateral. Whether this marsh supports black rails is unknown; however, the marsh is located more than 10 miles north of the East Highline Canal Seepage Recovery and In-line Reservoir project areas. A smaller (<0.15-acre), isolated marsh with surface water and emergent vegeta-tion is located on the west side of the canal, on the north side of the Orchid Lateral. This area is within the reach where seepage recovery units would be installed.

Greater Sandhill Crane. The greater sandhill crane is listed as threatened by CDFG due to habitat losses as wetlands have declined. Sandhill cranes are migrants and number less than 300 in Imperial Valley. Some are known to winter at roost sites located in shallow flooded ponds of a private duck club near Imperial (Radke, 1992). Both greater and lesser sandhill crane subspecies have been observed, with the majority of the birds having characteristics of the greater subspecies. Nesting occurs in north-western California and Oregon. Sandhill cranes have also been observed at other pri-vate ponds in the Imperial Valley, sometimes in association with the white-faced ibis. In the Imperial Valley cranes forage on agricultural fields.

Western Snowy Plover. The western snowy plover is proposed for federal listing as a Threatened species and is a California Species of Concern and a federal Category 2 species. Human disturbance of nesting sites has reduced numbers of this species. Snowy plovers are generally associated with estuarine shorelines and nest on sandy or gravelly beaches around alkali lakes in California, including the Salton Sea. Nesting occurs on undisturbed beach areas along the southern shore of the Salton Sea. Snowy plovers in the Imperial Valley consist of common residents and summer migrants to the Salton Sea, when up to 215 birds could visit the area. This species feeds on insects; amphipods, brine flies, and other invertebrates.

3.4-28

Mountain Plover. Mountain plover is a federal Category 2 species and a California Species of Concern. The mountain plover ranges from southern Alberta through por-tions of many western states (including Montana, North Dakota, Wyoming, Nebraska, Colorado, Kansas) and south into central California, New Mexico, Arizona, and coastal Texas (Ehrlich et al., 1992). Mountain plover are winter visitors to the interior valleys and plains of California including approximately 1,500 in the Imperial Valley (Grinnell and Miller, 1986). This species is found on shortgrass prairie at lower to moderate elevations and feeds primarily on insects. Mountain plover are at risk primarily due to conversion of shortgrass prairie habitat to agriculture (Ehrlich et al., 1992). In the Imperial Valley, mountain plovers forage for terrestrial insects on agricultural fields.

Long-Billed Curlew. The long-billed curlew is proposed for listing as a federal Endan-gered Species and is identified as a California Species of Special Concern because of declining populations potentially due to agricultural practices. Breeding occurs in northern California in late spring and summer. In the Imperial Valley, approximately 20,000 curlews migrate during the fall to winter until about April. They feed on such food items as aquatic organisms, insects, and vegetation taken by wading in freshwater wetlands or by foraging on agricultural fields.

Gull-Billed Tern. Gull-billed terns are a California Species of Special Concern. Nesting populations at the Salton Sea have declined as rising water has flooded island nesting sites. The present population of about 300 birds is expected to occur at the southeast part of the Salton Sea. Terns migrate to the area in April, generally departing by Sep-tember. They nest on open sandy flats either singly or in groups at the edge of colo-nies of other terns. The Salton Sea is the only California nesting site; additional nesting populations occur on the Gulf of California, Gulf of Mexico, and north Atlantic coasts. They are opportunistic feeders and eat terrestrial and aquatic invertebrates, amphib-ians, snakes, fish, small mammals, and eggs. Foraging habitat in the Imperial Valley are beach or mudflats of the Salton Sea and agricultural fields.

Caljfornia Least Tern. The California least tern is a state and federal Endangered spe-cies. Disturbance by humans and predation of chicks by cats, rats, red foxes, northern harriers, and other predators cause the species' decline. Least terns breed in colonies of 20 or more pairs on open, flat beaches on the southern California coast, San Fran-cisco Bay, and other shoreline. The nest is usually near shallow water where the tern forages for small fish and aquatic invertebrates. Although terns are occasionally observed during spring and summer and rarely in the fall in the Salton Sea area, no breeding colonies or self-sustaining populations are known (Grinnell and Miller, 1986; lID, 1986a).

SACsSC3O331I3.4 3.4-29

Black Tern. Black terns are a federal Category 2 species and a California Species of Concern. Black tern populations are decreasing throughout their North American range primarily through wetland loss and degradation. In addition, nesting success is often exceptionally low. Black terns feed on aquatic invertebrates and fish caught near the water surface, or flying insects found over meadows, marshes, and farmland. Black terns require fresh water for breeding and nesting sites. In California, nesting popula-tions of this wide-ranging species occur only in the northeastern part of the state (Ehrlich et al., 1992). They are common residents and migrants to Imperial Valley, estimated to be 10,000 individuals. Evidence of breeding at the Salton Sea is not known (CDFG, 1990). Foraging habitat in the Imperial Valley include beach or mud-flats of the Salton Sea and agricultural fields.

Black Skimmer. Black skimmers, a California Species of Special Concern, generally nest on unvegetated gravel bars, beaches, or small islands at the Salton Sea. The nesting sites of black skimmers are threatened by the rising level of the Salton Sea. Popula-tions have increased from initial nesting at the Salton Sea to approximately 600. Skimmers are tactile feeders that catch small fish and crustaceans by flying along the water surface and skimming their lower mandibles along the water. The CNDDB iden-tified nests on small exposed islands in the Salton Sea. Black skimmers are sensitive to human disturbance and will abandon nests after disturbances. Sightings reported to the CNDDB are given in Table 3.4-5 and shown in Figure 3.4-5. Foraging habitat consists of open water and beach or mudflats of the Salton Sea.

Burrowing Owl. The burrowing owl is a California Species of Special Concern. The species ranges widely in much of California but is generally uncommon where it does occur. The burrowing owl is a Species of Special Concern because of significant declines in populations in the Central Valley and San Francisco Bay regions. These declines are attributed in part to the encroachment of agricultural land by suburban development, ground squirrel control programs, habitat fragmentation, predation by feral animals, and wildfire prevention efforts in suburban areas (DeSante, 1992). Popu-lations of burrowing owls in the Imperial Valley are widespread and relatively common throughout the agricultural area numbering about 1,500 individuals. This species is found in open, dry grassland areas and forages largely on insects, along with small mammals, reptiles, birds, and carrion. Burrowing owls use existing burrows (especially ground squirrel burrows) for shelter and nesting cover (CDFG, 1992a). Burrowing owls are expected to occur throughout the project areas.

Loggerhead Shrike. Loggerhead shrikes are a federal Category 2 species and a Califor-nia Species of Concern. Populations of loggerhead shrikes have declined throughout the species' range over the last two decades. These declines have been attributed to habitat destruction, exposure to pesticides, and the impact of cars traveling along roads in nesting and hunting territories (Ehrlich et al., 1992). Shrikes require open habitats with sparse trees and shrubs that provide perches for hunting. They feed on large insects and small birds, mammals, amphibians, reptiles, fish, and carrion. They both breed and winter in much of the range that extends throughout most of North America from central Canada to south Mexico (Grinnell and Miller, 1986). Shrikes are common residents and winter visitors in foothills and lowlands throughout California and have been observed throughout the Imperial Valley.

3.4-30

Black-Tailed Gnatcatcher. The black-tailed gnatcatcher is a California Species of Con-cern. Decline of the species is attributed to habitat fragmentation and loss to urbariiza-tion. Much of the gnatcatchers' range has already been developed, and areas of native scrub remaining in open-space easements may be too small to support viable popula-tions. In addition, once an isolated patch of habitat is eliminated, gnatcatchers will probably not recolonize because they will seldom cross even narrow barriers of unsuit-able habitat (Ehrlich et al., 1992). Black-tailed gnatcatchers are year-around residents of desert wash habitat, although nesting is restricted to lowland, arid scrub. They feed on insects and spiders gleaned from foliage and twigs (Ehrlich et al., 1992; CDFG, 1990). They are commonly found along the Colorado River and in the Imperial Valley (Grinnell and Miller, 1986), and have been observed at the area upstream of the Water Conservation/Flood Control project area during field surveys in 1993.

Arizona Bell's Vireo. Arizona bell's vireo is a federal Endangered species. Decline of the species in California is attributed to a combination of riparian habitat loss and cowbird parasitism (Ehrlich et al., 1992). Bell's vireo was formerly a common summer resident in western Sierra Nevada, throughout the Sacramento and San Joaquin Val-leys, in coastal valleys and foothills south of Santa Barbara County, and along the entire length of the Colorado River. Arizona bell's vireo is now a rare summer resident along the Colorado River from Needles south to Blythe (CDFG, 1990). Bell's vireo feeds on insects gleaned from foliage and branches and some fruit. Although these vireos usually occur near water, they also inhabit thickets along dry intermittent streams. Potential occurrence in the ID project area is low and they are not known to occur in the Imperial Valley.

Large-Billed Savannah Sparrow. The large-billed savannah sparrow is a federal Category 2 species and a California Species of Concern. Sparrows are subject to predation by hawks, snakes, and small mammals. This species is a winter visitant (late August through early March) to California, migrating northwest from breeding grounds along the Gulf of California and Mexico (Grinnell and Miller, 1986). This species inhabits beaches, coastal marshes, grassland, saline emergent wetlands, and wet meadows from south of the Mexican border north to San Luis Obispo County. Large-billed savannah sparrows are uncommon winter visitors along the shores of the Salton Sea, and are primarily found in salt cedar scrub at river deltas (CDFG, 1990).

Bell's Sage Sparrow. Bell's sage sparrow is a federal Category 2 species and a California Species of Concern. This species is a possible winter visitor to the Salton Sea area. Summer and winter ranges extend along the coastal, scrub, and sage habitats from Trinity County south to Mexico. Winter visitors to the southeastern deserts generally arrive in October and depart by March. Sage sparrows feed primarily on insects, spiders, and seeds. They are preyed on by great horned owls, and declines may also be attributed to habitat degradation (Ehrlich et al., 1992; CDFG, 1990).

3.4-31

 

Section: 3.4.4 Aquatic Birds in the Imperial Valley

Aquatic birds in the Salton Sea area use water resources that are almost completely dependent on water management practices. Changed water management ,practices of IID and Imperial Valley farmers in the area could affect food and habitat abundance and diversity to varying degrees. The Imperial Valley area provides open water, shore-line river riparian, and terrestrial habitats and has become an important wintering area for waterfowl and shorebirds, including a number of special-status species (see Table 3.4-4).

The Salton Sea, designated wildlife areas, and adjacent Imperial Valley provide habitat for a great variety of birds. Approximately 375 species have been recorded for the area, and the Salton Sea NWR has the most diverse array of bird species found on any of the 400 NWRs (USEWS, 1987).

Irrigation Drains and Agricultural Fields. Avian wildlife use of the drains in ID varies with season and food availability. Drains provide little cover, and fish and invertebrate abundance can vary seasonally due to agricultural uses. When fields are inactive, drains may dry completely, eliminating aquatic populations. In spring and summer, popula-tions can fluctuate with flows and food availability. Therefore, the drains can be an important, although sporadic, food resource. Yuma clapper rails will pioneer areas for feeding, and the salt cedar and common reed stands may provide suitable foraging habitat for this species. Egrets, herons, and ibises in the area exploit sporadic food resources such as sudden emergence of invertebrates when fields are flooded. (Descriptions of the habitats along the drains are provided in Tables 3.3-3 through 3.3-13 in Section 3.3). Water-associated birds, including the clapper rail, are likely to use drains for foraging but will nest in other areas with suitable habitat. As with the Salton Sea, birds are at the highest trophic levels of biota associated with the New and Alamo Rivers, irrigation drains, and agricultural fields. Figure 3.4-2 illustrates the trophic relations among biota of these areas.

New and Alamo Rivers. The New and Alamo Rivers provide a corridor of river riparian habitat. The Finney-Ramer Unit of the Imperial Wildlife Management Area, which is adjacent to the Alamo River and East Lowline drains, provides nesting, foraging, and resting habitat for a variety of waterfowl and water-associated birds. Finney Lake pro-vides open water and cattail/bulrush marsh habitat for birds such as white pelicans, double-crested cormorants, and a number of ducks, grebes, gulls, and terns. Yuma clapper rails and brown pelicans are found at Finney Lake, and clapper rails nest in the marshes around the edges of the lake (Gonzales, 1992; Radke, 1992). About 30,000 egrets (great egrets, snowy egrets, and cattle egrets) currently nest at Finney Lake. Ramer Lake is being enhanced by CDFG and will provide approximately 1,200 acres of additional open water and wetland habitat. Clapper rails are associated with cattail stands for nesting, and the vegetation along the drains and the New and Alamo Rivers in the project area provides little nesting habitat for rails or other water-associated birds.

3.4-32

Salton Sea. Most waterfowl that winter in the Salton Sea area use the freshwater wet-lands associated with the mouths of the New and Alamo Rivers, creeks, and other freshwater outlets. The populations of waterfowl in the area are relatively stable. Waterfowl, marsh, and shore birds have adapted to the changing environment of the Salton Sea and Imperial Valley. Waterfowl were attracted to the marsh adjacenct to Salton Sea from former wintering habitat along the declining Colorado River delta. The expansion of irrigated farmiand and the expansion of the Salton Sea since 1904 caused bird populations to feed on crops for food. The Salton Sea NWR was created in part to provide forage areas for wintering waterfowl so they would not consume Imperial Valley crops.

Double-crested cormorants had previously nested at Salton Sea but are no longer found nesting there (Radke, 1992), possibly because of the loss of nesting habitat from inun-dation (attributable to the declining surface water elevation) or the loss of important food resources from declines in fish populations (attributable to increasing salinity). However, there is a considerable amount of uncertainty due to fluctuation in surface water elevation and the continued increase in salinity at the Salton Sea. Birds occupy the highest trophic levels of Salton Sea biota. Figure 3.4-1 illustrates the trophic rela-tions found in Salton Sea biota.

Average use of the Salton Sea by cormorants, herons, egrets, and other species at the Salton Sea has also been estimated by USFWS (1993 a). Using USFWS data, approxi-mate numbers for various species are on the order of 200 double-crested cormorants, 90 great blue herons, 160 great egrets, 350 snowy egrets, and 260 black-crowned night-herons, for representative species that are year-round residents at the sea, but whose maximum numbers also include winter residents in addition to breeding-season birds. Setmire et al. (1993) also included estimated numbers for these species (see Table 3.4-1) that are somewhat higher than those derived from the USFWS bird-use data.

Unlike pelicans and some of the other piscivorous species, herons and egrets, as well as terns and black skimmers, nest in various locations at the Salton Sea (USEWS, 1993a). The USEWS has conducted annual surveys of these colonially nesting species (as well as cormorants, which apparently have not nested at the Salton Sea since 1988 [i.e., nesting ceased during "pre-project" years]; see Table 3.4-6) although the birds are pres-ent during the nesting season. The total number of active nests for these species listed in Table 3.4-6 during 1992 was at least 906. Counts for some species are incomplete in earlier years because those species did not nest in the traditionally surveyed areas and data are incomplete. Cormorants, herons, and egrets typically nest in trees or shrubs, whereas the terns and skimmers nest on the ground.

3.4-33

Table 3.4-6
Summary of Colonially Nesting Birds at Salton Sea, 1987-1992
Number of Active Nests

Species

1987
1988
1989
1990
1991
1992

Double-crested cormorant

63
57
0
0
0
0

Great blue heron

261
211
10
19
20
104

Great egret

105
292
93
118
151
221

Snowy egret

109
49
260
226
160
198

Cattle egret

1,873
1,700
798
42
25
55

Black-crowned night heron

--
--
--
--
--
117

Gull-billed terna

--
--
--
--
--
89

Caspian terns

--
--
--
--
--
35

Black skimmer

--
--
--
--
--
87

Species nesting in areas not surveyed in some years before 1992.
Source: USFWS (1993d).

Bird Die-Offs. A major die-off of eared grebes occurred at the Salton Sea from mid-January to early April 1992. Based on USFWS shoreline surveys, aerial surveys, and clean-up efforts, it is estimated that 150,000 eared grebes died during this period (Audet, 1992). Although the cause of the eared grebe die-off has not been determined, an estimated 5,000 birds, including 47 species such as ruddy duck, ring-billed gull, eared grebe, northern shoveler, snow goose, and numerous shorebirds, died of avian cholera from January to March 1992. This type of cholera die-off has been documented at the Salton Sea in the past (Audet, 1992), but avian cholera outbreaks also occur frequently in many other areas of the United States (Friend, 1987).

The cause of the eared grebe die-off (aside from some mortality to avian cholera) is unknown, although the typical causes of large-scale bird die-offs have been examined through a series of tests and analyses (Audet, 1992). All types of avian botulism, viral diseases, and salt toxicosis were ruled out as the cause of the die-off. Endrin, organo-phosphate pesticides, mercury, and selenium were identified as contaminants potentially responsible. However, endrin was ruled out because all tissue samples had non-detect-able levels of this organochlorine pesticide. Organophosphates were ruled out because eared grebe brain samples had normal levels of cholinesterase (inhibition of this brain enzyme indicates organophosphate or carbamate exposure).

Tissues of dead, sick, and healthy grebes were collected and analyzed for mercury, sele-nium, and other trace elements. None of those elements was in the range where acute toxicity would be expected (Goodbred, 1992).

Constituents of Concern in Birds. Setmire et al., 1993, identified selenium, boron, and DDT metabolites as major contaminants in the Imperial Valley area. Of the 375 docu-mented bird species in Imperial Valley, Table 3.4-7 lists 127 of these species that could be subjected to actual or potential adverse effects related to drainwater (Setmire et al., 1993). A further assessment was made to determine a "level of concern" for each of the 127 species. A high concern was assigned if the contaminant concentration in a major food item of a species was greater than any documented threshold. A low con-cern was assigned if a major food item had a contaminant concentration less than a threshold but above analytical limits, or if a minor food item had a contaminant con-centration above a threshold. No concern was assigned if contaminant coicentrati'bn~ in all or most food items were at or near background concentrations.

3.4-34

Table 3.4-7

Summary of Agriculture-Related Contaminants of Concern for Birds that Feed In the Salton Sea and Associated Rivers and Drains Contaminants of Concern

Sheet 1 of 3

Species
Contaminants of Concern
Selenium
Boron
DDE

Podicipedsdae-grebes

Pied-billed grebe

H
L
L

Eared grebe

H
L
L

Western grebe

H
L
L

Clark's grebe

H
L
L

Pelecanidae-pelicans

American white pelican

H
--
H

California brown pelican

H
--
H

Phalacrocoracidae-cormorants

Double-crested cormorant

H
--
H

Ardeidae-bitterns and herons

American bittern

L
--
L

Least bittern

H
--
H

Great blue heron

H
--
H

Great egret

H
--
H

Snowy egret

L
--
H

Cattle egret

H
L
H

Green-backed heron

H
--
H

Black-crowned night-heron

H
--
H

Threskiornithidae-ibises

White-faced ibis

L
L
H

Ciconiidae-storks

Wood stork

H
--
L

Anatsdae-waterfowl

Fulvous whistllng duck

L
H
--

Snow goose

--
L
--

Ross' goose

--
L
--

Canada goose

--
L
--

Green-winged teal

L
H
--

Mallard

L
H
--

Northern pintail

L
H
--

Cinnamon teal

L
H
--

Northern shoveler

H
H
--

Gadwali

H
H
--

Canvasback

H
H
--

Redhead

H
H
--

Lesser scaup

H
H
--

Bufflehead

H
H
--

Ruddy duck

H
H
--
3.4-35

Table 3.4-7

Summary of Agriculture-Related Contaminants of Concern for Birds that Feed In the Salton Sea and Associated Rivers and Drains Contaminants of Concern

Sheet 2 of 3

Species

Contaminants of Concern

Selenium
Boron
DDE

Cathartidae-vultures

Turkey vulture

--
--

H

Accipitridne-osprey, eagles, and hawks

Osprey

H
--
H

Bald eagle

H
--
H

Northern harrier

--
--
H

Sharp-shinned hawk

--
--
L

Cooper's hawk

--
--
L

Red-tailed hawk

--
--
L

Falconidae&emdash;falcons

American kestrel

--
--
H

Peregrine falcon

--
--
H

Prairie falcon

--
--
H

Rallidae-rails, moorhens, coots

Yuma clapper rail

H
H
L

Virginia rail

L
L
L

Sora

L
H
--

Common moorhen

L
H
--

American coot

H
H
--

Gruidae-cranes

Sandhill crane

L
--
H

Charadrudae-plovers

Black-bellied plover

L
L
L

Snowy plover

L
H
L

Semipalmated plover

L
L
L

Killdeer

L
L
H

Mountain plover

--
--
H

Recurvirostridae-silts and avocets

Black-necked stilt

H
L
H

American avocet

H
L
L

Scolopacidae-sandpipers and phalaropes

Greater yellowlegs

L
L
L

Lesser yeilowlegs

L
L
L

Willet

L
L
--

Spotted sandpiper

L
L
--

Whimbrel

L
L
L

Long-billed curlew

L
--
H

Marbled godwit

L
L
--

Red knot

L
L
--
3.4-36

Table 3.4-7

Summary of Agriculture-Related Contaminants of Concern for Birds that Feed In the Salton Sea and Associated Rivers and Drains Contaminants of Concern

Sheet 3 of 3

Species

Contaminants of Concern

Selenium
Boron
DDE

Sanderling

L
L
--

Western sandpiper

L
L
--

Least sandpiper

L
L
--

Dunlin

L
L
--

Stilt sandpiper

L
L
--

Short-billed dowitcher

L
L
--

Long-billed dowitche

L
L
--

Common snipe

L
L
L

Wilson's phalarope

L
L
--

Red-necked phalarope

L
L
--

Laridae-gulls, terns, skimmers

Laughing gull

H
--
H

Bonaparte's gull

L
L
H

Ring-billed gull

L
--
H

California gull

--
--
H

Herring gull

H
--
H

Yellow-footed gull

H
--
H

Gull-billed tern

L
H
L

Caspian tern

H
--
H

Common tern

H
L
H

Forster's tern

H
--
H

Black tern

L
L
H

Black skimmer

H
--
H

Cuculidae-cuckoos and roadrunners

Great roadrunner

--
--
H

Strigidae-owls

Barn owl

--
--
H

Burrowing owl

--
--
H

Alcedinidae-kingflshers

Belted kingfisher

H
--
H

Troglodytidae-wrens

Marsh wren

L
L
L

Motacillidae-pipits

American pipit

L
--
H

Emberizidae-wood warblers (in part)

Common yellowthroat

L
L
L

Note: Agriculture-related contaminants of concern (level of concern): H, high;
L, low, --, no concern.
Source: modified from Setmire et al., 1993.

3.4-37

In summary, the groups at greatest risk (in order of highest to lowest concern) are:

(1) piscivorous birds&emdash;for which there is a high level of concern for effects of selenium, primarily in the Salton Sea, and DDE throughout all aquatic habitats in the Imperial Valley; (2) waterfowl&emdash;for which levels of concern are high for selenium and boron in aquatic habitats; (3) shorebirds&emdash;for which levels of concern are variable for selenium and boron in all aquatic habitats and DDE in rivers and drains; and (4) terrestrial birds&emdash;for which levels of concern are high for DDE.

Selenium. Selenium concentrations have been measured in birds from the Imperial Valley or Salton Sea in four studies conducted since 1985. These include the Selenium Verification Study by CDFG (White et al., 1987), the reconnaissance investigation by the U.S. Department of the Interior (USD1) (Setmire et al., 1990), a sampling of night-heron and egret eggs by USFWS (Ohlendorf and Marois, 1990), and a more extensive study by the USD1 (Schroeder et al., 1993; Setmire et al., 1993). An earlier study was designed to evaluate the effects of geothermal development in the Imperial Valley on wintering waterfowl (Koranda et al., 1979). Results of these studies, summarized below, indicate that birds bioaccumulate selenium at elevated levels through feeding on aquatic organisms in the Imperial Valley and Salton Sea area. In sediments, highest concentrations of selenium were found in the Salton Sea (Setmire et al., 1990,1993). Sediments in the Salton Sea are the principal food-chain pathway of selenium bio-accumulation; high concentrations of selenium in Salton Sea sediments probably account for the elevated levels of selenium found in birds in the region.

Migratory birds may acquire selenium in other areas (such as the San Joaquin Valley), but selenium concentrations in tissues of nesting birds, their eggs, and pre-fledgling juveniles tend to reflect exposure at the sampling location because the birds are less mobile during their nesting period (Ohlendorf, 1989; Ohiendorf et al., 1990; Skorupa and Ohlendorf, 1991). In addition, selenium is rapidly depurated from bird tissue if the selenium source is removed (Heinz et al., 1990; Heinz, 1993; Heinz and Fitzgerald, 1993a).

According to the Selenium Verification Study, double-crested cormorants from the Salton Sea had significantly higher mean selenium concentrations (about 33 ~ dry weight) in their livers than did cormorants from San Francisco Bay and Humboldt Bay (about 17 ~ probably because of high levels in their diet composed mostly of fishes (tilapia, croakers) from the Salton Sea (White et al., 1987). Lesser scaup, apparently feeding on barnacles at the Salton Sea, did not contain proportionately elevated selen-ium levels compared to levels in fish and fish-eating birds. Levels were similar to levels found in scaup in Humboldt Bay and parts of the San Francisco Bay system, and signif-icantly less than scaup from Suisun Bay. American wigeon from the Salton Sea hadhigher selenium levels in muscle than reported in the literature for other dabbling ducks but less than one-third the average levels in ducks (no wigeon) at Kesterson NWR in 1983 and 1984. Selenium levels in livers of black-necked stilts from the Salton Sea (about 17 mg/g) were significantly higher than in stilts from Grizzly Island and Gray Lodge Wildlife Areas and Sacramento NWR (about 8 mg/g) but much less than in stilts from Kesterson NWR (42 to 95 mg/g) where stilt reproduction was affected by selenium (Ohlendorf et al., 1990) and waterborne selenium concentrations were highly elevated (averaging about 300 mg/L compared to Imperial Valley irrigation drainage levels of 6 to 9 mg/L; Ohlendorf, 1989).

3.4-38

In the reconnaissance investigation, selenium was detected in livers of aquatic birds at concentrations up to 27 mg/g in black-necked stilts from the New River delta and 42 mg in double-crested cormorants from the Alamo River delta (Setmire et al., 1990). Other stilts from the Whitewater River delta (19 mg/g) and Alamo River delta (20 mg/g) had selenium levels that were similar to those from the New River. Other cormorants from the New River at Rio Bend (21 mg/g) and Alamo River delta in 1986 (18 mg/g) had lower selenium levels than those in 1987.

Selenium concentrations in cattle egrets from the New River at Rio Bend (6.7 mg/g) and the Trifolium/Vail drains (5mg/g) were not elevated in comparison to normal levels for birds at freshwater reference sites (data from Skorupa et al., 1990). Selenium concentrations in coots were 8.3 to 21 mg/g or various locations, and in great blue herons they were 15 mg /g, all of which were about twice the normal levels.

Migratory waterfowl (including northern shovelers and ruddy ducks) and herring gulls from the Imperial Valley and Salton Sea also had moderately elevated concentrations of selenium that ranged up to 27mg/g in one composite sample of ruddy duck livers. Selenium concentrations in shovelers during 1986 (Setmire et al., 1990) were similar to those found in green-winged teal (15 mg/g), northern shovelers (15.6 mg/g), and northern pintails (11.2 mg /g) in the earlier study (Koranda et al., 1979). However, the selenium concentrations in those composite samples of ruddy duck livers during 1986 (7, 19, and 27 mg /g) were much lower than in ruddy duck livers collected previously (49.5 mg/g) by Koranda et al. (1979).

Selenium concentrations in eggs of black-crowned night-herons and great egrets from the Salton Sea area were analyzed in 1985 (Ohlendorf and Marois, 1990), and they apparently provide the oniy published measurements of selenium in eggs of fish-eating birds from this area. Mean selenium concentrations in night-heron eggs collected from the Whitewater River delta (1.10 mg /g, wet weight) were significantly higher than in night-heron eggs from three locations in the San Joaquin Valley and in great egret eggs (0.643 mg /g, wet weight) collected from a colony near the mouth of the New River. The selenium concentrations in all night-heron and egret eggs were below those associ-ated with reproductive effects in night-herons or mallards, so reproductive effects are not likely to have occurred in night-herons or egrets. Eggs of various fish-eating bird species (including herons, egrets, and black skimmers) were sampled by the USFWS during 1991 in its Piscivorous Bird Study at the Salton Sea (Rivera, 1994).

3.4-39

Although only preliminary results are available, the average concentrations of selenium seem to be between 3.5 and 6.5 mg/g dry weights (about 0.75 to 1.6 mg /g wet weight).

In the USD1 detailed study of selenium (and other chemicals) in the Salton Sea area during 1988-1990, several species of aquatic birds (or their eggs) were sampled at vari-ous locations. Selenium exposure and potential effects in birds can be assessed most directly through the selenium concentrations in eggs (Skorupa and Ohlendorf, 1991), and black-necked stilts were the oniy species for which eggs were sampled by Schroeder et al. (1993) and Setmire et al. (1993). Stilt eggs were analyzed from nine locations (Table 3.4-8). Geometric mean concentrations were 6.2mg/g or less at all locations, indicating that exposure of the stilts to selenium ranges from background (Salton Sea at the New River delta) to about twice normal background (at Reidman Pond freshwater impoundment and at McKendry Road). All stilt eggs contained <8 mg/g selenium except for one or two eggs at four locations (10 mg/g on the New River, 13 and 35 mg/g at Reidman Pond, 9.6 mg/g at Hazard Pond freshwater impoundment, and 14 mg /g at McKendry Road); females that laid those eggs probably had greater exposure at a different location than the other stilts within a week or two of laying their eggs.

 

Table 3.4-8
Summary of Geometric Mean p,p'-DDE Concentrations
in Black-Necked Stilt Eggs
Location
p,p'-DDE Concentration
(µg/g wet wt.)

B1: Salton Sea National Wildlife Refuge - Unit 1 1.3

1.3

B15: New River delta 1.6

1.6

B17: New River at Rio Bend

2.8

B24: Trifolium 14

2.5

B25: Vail Cutoff

0.5

B34: RH Pond

6.3

B36: Reidman Pond

5.1

66B37: Hazard Pond

4

B39: McKendry Road

1.9

Source: Schroeder et al. (1993).

Selenium concentration in liver and muscle tissue of birds sampled during the USDI detailed study is shown in Table 3.4-9. Selenium levels in some aquatic birds are in the range of concern and suggest that adverse biological effects may have occurred, but they have not been documented (White et al., 1987; Setmire et al., 1990, 1993; Schroeder et al., 1993). No studies have been completed in the Salton Sea area to determine if selenium has caused effects such as those observed in other areas contami-nated by selenium from agricultural drainwater, although the Piscivorous Bird Study by the USFWS should provide additional data (Rivera, 1994).

3.4-40

Table 3.4-9
Summary of Geometric Mean Selenium Concentration. (mg/g dry weight) in Selected Species of Birds Taken from Salton Sea and Nearby Area (1988.1990)
Location
Species
American coot
Black-Necked
Stilt

Earbed
Grebe

Northern Shoveler

Ruddy Duck

White-Faced Ibis

(liver)
(muscle)
(liver)
(muscle)

Salton Sea

B1: Salton Sea National Wildllfe Refuge - Unit 1

na
4.8
na
15.3
na

12.4

4.9
na

B11:Alamo River delta

na
na
na
17.1
na
na
na
na

B13: Obsidian Butte

na
na
33.5
na
na
na
na
na

Rivers

B17:New River at RioBend

na
4.0
na
na
na
na
na
na

Irrigation Drain.

B24: Trifolium 14

na
na
4.6
na
10.6
na
na
na

B25: vail Cutoff

10.3
3.9
na
na
na
na
na
na

B26:VaiI 4

na
na
na
na
6.4a
na
na
na

Freshwater Impoundments

B33:ShadyAcresDuckClub

na
na
na
13.0
3.9
na
na
na

B34:RHPond

na
3.9
na
na
na
na
na
na

B35:HQPond

na
na
na
na
na
na
13.4
4.1

B36: Reidman Pond

na
6.2
na
na
na
na
na
na

B37: Hazard Pond

na
4.9
na
28.3
6.0
10.6
na
na

Imperial Valley

B38:South Brawley

na
na
na
na
na
na
na
7.4

B39:McKendryRoad

na
6.0
na
na
na
na
na
na

aSelenium concentration based on single detect
na: Not analyzed at this location.
Source Schroeder et al. (1993).

3.4-41

Food-Chain Relations. In the Imperial Valley, dissolved selenium from sources such as irrigation drainwater first is incorporated into lower trophic levels of the Salton Sea's aquatic ecosystem such as plants and invertebrates. From there, the pathway can go directly into small forage fish and then birds, or biologically incorporated selenium c~an be deposited into the sediment. Selenium that has accumulated in sedim~nt then can be cycled back into biota and remain at elevated levels for years after selenium input has ceased (Setmire et al., 1993).

The most important selenium food-chain pathway in the Salton Sea begins with accum-ulation by benthic invertebrates, particularly pileworms, and includes subsequent uptake by benthic-feeding fish and fish-eating birds (Figure 3.4-6). Selenium is transferred from sediment through successive trophic levels in the food chain at increasing concentrations, which shows that biomagnification occurs (Setmire et al., 1993).

 

Figure 3.4-6: Selenium Cycle in the Salton Sea
(Source: Stemire et al., 1993)

3.4-42

3.4-43

Figure 3.4-7: Concentration of Selenium in Food-Chain Organisms of the Salton Sea, 1988-1990, and Dietary Thresholds for Water Birds
Source: Setmire et al., 1993

In general, lower trophic-level consumers in the Salton Sea have concentrations of selenium that are 2 to 6 times higher than those of primary producers (Figure 3.4-7). As selenium concentration increases up the food chain, thresholds for water bird food items (Heinz and others, 1989, 1989) are exceeded only in larger forage fish and preda-tory fish. Therefore, the larger fish-eating birds such as brown pelicans and double-crested cormorants are at greatest risk (Setmire et al., 1993).

Biological selenium pathways in rivers and drains of the Imperial Valley are shown in Figure 3.4-2. In comparison with the selenium pathway in the Salton Sea, less bio-accumulation occurs at the highest trophic levels. Large birds feeding in rivers do not accumulate nearly as much selenium as those feeding in the Salton Sea. In rivers and drains, selenium enters the food chain through water, and accumulation from sediment is much less than in the Salton Sea. In contrast, many fish-eating birds such as double-crested cormorants feed almost exclusively in the Salton Sea and consume fish that may have elevated selenium concentrations (Setmire et al., 1993).

Selenium bioaccumulation in food chain organisms of rivers and drains (Figure 3.4-8) is similar to that for Salton Sea food chains, but with lower values at similar trophic levels. Concentrations at the highest freshwater trophic level are only one-half those in the Salton Sea. For birds feeding in rivers and drains, mean selenium concentrations for all trophic levels are at or below the possible threshold that threatens survival. However, the range of concentrations for some species, especially forage fish, extends well above the area-of-concern threshold (4 mg/g dry weight). Birds feedi~ig on these freshwater fish could be exposed to concentrations that affect reproduction (greater than 7 mg/g dry weight) and actual long-term survival (greater than 10 mg/g dry weight) (Setmire et al., 1993).

3.4-43

 

 

Figure 3.4-8: Concentration of Selenium in Food-Chain Organisms of Rivers and Drains in the Imperial Valley, 1988-90, and Dietary Thresholds for Water Birds
(Source: Setmire et al., 1993)

 Boron. Boron concentrations up to 52 mg/g were reported for livers of resident water birds from the Salton Sea area (Setmire et al., 1990). However, there was no apparent correlation between drainwater-affected sites and occurrence of the elevated boron concentrations. Liver concentrations of boron were higher in migratory water birds than in the resident water birds because the migratory birds sampled feed on a higher proportion of vegetation that has high boron concentrations (Setmire et al, 1993). Boron data for ruddy ducks indicate that birds arrive at the Salton Sea with moderately low levels (mostly nondetectable) of boron and that some individuals depart with levels known to cause adverse reproductive effects. Although resident shorebirds (i.e., black-necked stilt) generally bioaccumulated less boron than waterfowl, boron accumulation in shorebirds may be sufficient to cause reduced weight gain in young. Piscivorous birds feeding at the Salton Sea also may be bioaccumulating boron at levels known to cause reproductive effects (Setmire et al., 1993).

3.4-44

Boron concentrations in bird eggs from the Salton Sea area were 6mg/g or less (Schroeder et al., 1993). In experimental studies with mallards (Smith and Anders, 1989; PWRC, 1990; Smith and Heinz, 1990), dietary boron concentrations up to 450 µg/g did not affect egg hatchabilty, but duckling weight gain was reduced when the adults and their ducklings had a dietary boron concentration of 288 mg/g. Boron con-centrations in the livers of these mallards averaged 15 mg/g in adults and 17 mg/g in ducklings; eggs had a mean concentration of 13 mg/g. Boron concentrations in sago pondweed from the Trifolium/Vail Drains during 1986 was 370 mg/g (Setmire et al., 1990). Thus, the concentrations of boron in some bird livers and in aquatic plants suggest that sublethal effects could occur. However, algae and other plants sampled by Schroeder et al. (1993) and Setmire et al. (1993) usually had lower boron concentra-tions, and no adverse effects have been documented to occur in birds from the Imperial Valley.

DDT and Metabolites.

Migratory Birds. Waterfowl using drains and rivers are exposed to higher levels of DDT metabolites than waterfowl that primarily forage at the Salton Sea. Northern shovelers from drains and rivers had higher DDE concentrations in muscle tissues than eared grebes and ruddy ducks from the Salton Sea (Setmire et al., 1993). Birds of other trophic levels had similar concentrations of DDE residues in river and drains when compared to levels in Salton Sea species.

In the Imperial Valley, dietary intake may expose waterfowl to DDE concentrations of 0.01 to 5.7mg/g wet weight as shown in Table 3.4-10 (Setmire et al., 1993) Adverse health effects on reproduction of waterfowl have been noted when the diet contained 2.8 to 3.0 mg/g wet weight of DDE. Waterfowl foraging at the Salton Sea may be ex-posed to plant material and invertebrates that have DDE concentrations in excess of 2.8 mg/g. Dietary DDE concentrations of fish-eating birds may also exceed the 2.8 mg/g threshold, as well as levels established in 1973 by the National Academy of Sciences, National Academy of Engineering for the protection of predators (1.0 mg/g wet weight for freshwater species and 0.05 mg/g wet weight for saltwater species) as shown on Figure 3.4-9 (Setmire et al., 1993).

Birds foraging in agricultural fields had some of the highest DDE concentrations in liver and fat tissues detected in Imperial Valley birds (Setmire et al., 1993). White-faced ibis that winter in the Imperial Valley had DDE concentrations (geometric mean) of 5.93 mg/g wet weight in the liver and 5.57 mg/g wet weight in fat. These levels are similar to those in ibis egg collected at Carson Lake, Nevada, where reproductive problems have been observed (Setmire et al., 1993). Egg contaminant levels may be indicative of liver and tissue burdens derived from wintering ground exposure that occurs prior to the formation of the egg (Ohiendorf et al., 1993).

Other wintering birds that forage at the Imperial Valley and Salton Sea before migra-tion northward may also be exposed to DDE. Elevated levels of DDE in white peli-can eggs collected in the Klamath Basin may be indicative of birds exposed while wintering in the Imperial Valley (Setmire et al., 1993). A dietary intake of 0.15 mg/g total DDT has been associated with eggshell thinning in the endangered California brown pelican (Anderson et al., 1975). The increasing numbers of California brown pelicans foraging on Salton Sea fish are exposed to high levels of DDT and metabolites which may result in an increased DDE concentrations in eggs, leading to a corresponding increase in eggshell thinning and decrease in reproduction success (Setmire, et 4 1993).

3.4-45

Table 3.4.10
p,p'-DDE Concentration in Biota from the Salton Sea Area, 1986-90
Sample Type
Salton Sea
New, Alamo, and Whitewater Rivers and Irrigation Drain

N/DV

GM

Range

N/DV

GM

Range

Migratory Birds

Eared grebe
(muscle)
5/5
0.28
0.17-1.10
--
--
--
Northern shoveler
(muscle)
--
--
--
6/6
-0.55
0.17-2.10
Ruddy duck
(muscle)
30/30
0.26
0.096-1.50
--
--
--
White-faced ibis
(fat)
(liver)
--
--
--
9/9
5.57
3.70-11.0
--
--
--
9/9
5.93
3.10-9.60

Resident Birds

American coot
(liver)
(muscle)
--
--
--
3/3

0.014

0.01-0.03
--
--
--
4/4
0.22
0.09-0.45
Barn owL
(muscle)
--
--
--
1/1
--
2.7
Black-necked stilt
(egg)
(carcass)
84/84
2.54
0.05-12.0
--
--
--
38/38
0.69
0.02-2.76
--
--
--
Cattle egret
--
--
--
2/2
2.3
2.20-2.40
Double-crested cormorant
(muscle)
3/3
1.13
0.38-4.90
--
--
--
Great blue heron
(muscle)
--
--
--
1/1
--

13.0

Herringgull

1/1
--
2.80
--
--
--

Note: Concentrations in micrograms per gram, wet weight --, no data; N, number of samples collected DV, number of samples with detectable values; GM, geometric mean (calculated using 1/2 detection limit when data set has more than 50 percent detectable values).
Source: modified from Setmire et al., 1993.

3.4-46

 

Figure 3.4.9: Concentration of Total DDT for Three Species of Fish from the Salton Sea. 1988-90, and Dietary Thresholds for Fish-Eating Birds and Mammals Threshold for Effects on Fish Eating Birds and mamals from National Academy of sciences, National Academy of Engineering (1973). Threshold for Reduced Eggshell Thickness in Brown Pelican from Anderson and Others (1975).
(Source: Setmire et al., 1993)

Three raptors that are uncommon winter migrants to the Salton Sea area - osprey and the endangered bald eagle and peregrine falcon may also be exposed to high concen-trations of DDE in their diet of fish, shorebirds, and waterfowl (Setmire et al., 1993). Population declines of these species due partly to eggshell thinning and reproductive failure were caused by DDE accumulation. Foraging at the Salton Sea may expose these birds during migration periods.

Resident Birds. As shown on Table 3.4-10, resident birds had higher DDE con-centrations than migrant species because resident species are exposed to DDE in the diet throughout the year. Black-necked stilts had the highest tissue levels of birds sam-pled in the study. Muscle tissue from double-crested cormorants from the Salton Sea had elevated DDE concentrations (Table 3.4-11) at levels similar to observations from other heavily contaminated areas (such as the Houston Ship Channel), but not as high as concentrations detected in lower Colorado River cormorants (Setmire et al., 1993). The DDE concentrations in cormorants were 5 to 11 times higher than observed in Salton Sea fish tissues (bairdiella, tilapia), however, but these bioaccumulation factors were lower than observed in the Houston Ship Channel study (27 times).

3.4-47

Table 3.4-11
p,p'-DDE Concentrations in Cormorant Tissues from the Salton SeaArea and From Contaminated Sites in the Southern and Western United States
Species
Location
N/DV
GM
Range

Double-crested cormorant

Salton Sea

3/3
1.13
0.38-4.9

Houston Shipping Channel

10/10
0.93
0.40-2.3

Lower Colorado River

9/9
4.3
2.10-6.6

Olivaceous cormorant

Houston Shipping Channel

10/10
0.80
0.20-2.5

Note: Concentrations in micrograms per gram, wet weight. Values for Houston Shipping Channel from King (1989a) and for lower Colorado River from Radtke and others (1988). N, number of samples analyzed; DV, number of samples with detectable values; GM, geometric mean.
Source: Setmire et aL, 1993.

Egg samples collected for DDE analysis were restricted to black-necked stilts because of recent decline in nesting activity of fish eating birds throughout the Salton Sea area as shown in Table 3.4-12. It is estimated that the number of active waterbird nests at the Salton Sea has declined by 80 percent during 1986-1991 (Setmire et al., 1993). Decreased hatching success of black skimmer eggs has been correlated with elevated DDE concentrations. Black skimmer populations at the Salton Sea have declined by 40 percent since 1987. Although the reason for this decline is unknown, contaminants are suspected as contributing factors (Setmire, et al, 1993). Black-necked stilt eggs collected at the Salton Sea had DDE concentrations more than twice the levels observed in samples collected in the southern San Joaquin Valley as shown in Figure 3.4-10. In stilt egg collected from the Salton Sea locations shown in Table 3.4-13, the mean DDE concentration was higher than the 2.0 mg/g threshold associated with eggshell tbinning in osprey eggs, but below the 3.0 mg/g wet weight that caused reproductive impairment in California brown pelican populations (Setniire, et al, 1993). However, samples from some locations had mean DDE concentrations that were greater than those threshold levels.

Comparison of snowy egret eggshells collected in 1975 and pre-1953 museum specimens suggests that DDE residues have caused significant reproductive effects in colonial nesting birds throughout the Imperial Valley (Setmire et al., 1993). Birds are exposed to increased DDE concentrations at all tropic levels in the Imperial Valley (Figure 3.4-11) and at the Salton Sea (Figure 3.4-12), with the higher exposure occurring for fish-eating birds and birds of prey. Water birds and shorebirds forage on invertebrates with DDE concentrations that range from 0.01 to 0.68 mg/g wet weight, while fish-eating birds, such as pelicans and cormorants, are taking food items containing DDE concen-trations up to 5.7 mg/g wet weight. Birds of prey may ingest food with DDE levels as high as 21 ~ wet weight, and are at the greatest risk of reproductive problems if they feed consistently on those contaminated prey.

Bioaccumulation of DDE may expose resident birds to higher levels of contamination. Black-necked stilts foraging on pileworms and waterboatman with low DDE concen-trations (0.01 to 0.07 mg/g wet weight) may have bioaccumulation factors as high as 1200 (Setmire et al., 1993). The study concluded that even relatively low dietary concentrations of DDE residues may be exposing resident and migratory birds to potential reproductive problems and that declines in colonial waterbird nesting may be linked to increased DDE exposure in the Imperial Valley.

SA3.4-48

Table 3.4.12
Active Nests of Colonial Waterbirds at Major Rookeries Among the Salton Sea Shoreline, 1986-1991
Species
Number of Active Nests

1986
1987
1988
1989
1990

Black-crowned night heron

5
12
0
35
98

Cattle egret

2,094
1,873
1,700
798
42

Double-crested cormorant

24
63
57
0
0

Great blue heron

362
261
211
10
19

Great egret

49
105
292
93
118

Green-backed heron

0
0
2
0
4

Snowy egret

76
109
49
260
226

Total

2,610
2,423
2,311
1,196
507

Note: Based on N.D. Hogg, Santa Monica College, Santa Monica, California communication, 1992; and U.S. Fish and Wildlife Service, written communication, 1992
Source: Setmire et aL, 1993.

Figure 3.4-10: Concentration of p,p-DDE in Black-Necked Stilt Eggs from the imperial Valley, 1988-90, and Reproductive Impairment Thresholds for Selected Bird Species.
(Source: Setmire et al., 1993)

3.4-49

Table 3.4.13
p,p'-DDE Concentration in Black-Necked Stilt Eggs from Neighborhoods in the Imperial Valley, 1988-1989
Site No.
Location
Number of Samples
Mean p-p'-DDE Concentration
Group
B25

Vail Cutoff Drain

5
1.00
A
B15

New River Delta

10
1.97
AB
B39

McKendry Road

5
2.41
ABC
B1, B24

Salton Sea NWR (Unit 1) and Trifolium 14 Drain

15
2.57
ABCD
B17

New River at Rio Bend

27
3.33
ABCDE
B37

Hazard Pond

9
4.60
BCDEF
B36

Reidman Pond

4
6.10
CEF

B34

RHPond

9
6.46
F

Note: Location of sites shown in Figure 3.4-5. Concentrations in micrograms per gram, wet weight. Group: homogeneous groups determined at 95 percent confidence interval using Tukey's multiple comparison test (Statgraphics, 1988).
Source:Setmire et al., 1993.

 

 

Figure 3.4-11: Concentration of p,p-DDE in Food-Chain Organisms of the Salton Sea, 1988-1990, and Dietary Threshold for Predators. Adverse-Effects Threshold from National Academy of Sciences, National academy of Engineering (1973).
Source: Setmire et al., 1993.

3.4-50

Figure 3.4-12: Concentration of p,p'-DDE in Food-Chain Organisms of Rivers and Drains in the Imperial Valley, 1988-90, and Dietary Threshold for Predators. Adverse-Effects Threshold from National Academy of sciences, National Academy of Engineering (1973).
(Source: Setmire et al., 1993)

3.4-51

Bibliography

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