Table of Contents
Special Status Wildlife Species Use of Rice Cultivation Lands In California's Central Valley
Chapter 2 - Habitats In California
Early in the 19th century, the Central Valley consisted of large numbers of small creeks, sloughs, and oxbows that, along with the major rivers, were subjected to periodic flooding. During these periods, sinks were formed that remained undrained except during periods of high water. The scouring associated with seasonal flooding created a mosaic of channels, depressions, lowland swamps, marshes, and hummocks across wide expanses of the Central Valley (Scott and Marquiss 1984). Extensive grasslands, riparian, and valley oak forests together formed a complex diversity of habitats that supported enormous flocks of ducks, geese, swans, cranes, shorebirds and a host of other species. Today, most of the original habitat has been lost to urbanization, agricultural conversion, water diversion, and levee construction.
An estimated 95 percent of the 4 million acres of California's historic wetlands have been destroyed or seriously modified within the last 100 years (Gilmer et al. 1982). In spite of this appalling loss of habitat, 3 to 5 million ducks, geese, and swans winter in California. During their annual cycle, large numbers of shorebirds, cranes, pelicans, egrets, herons, ibises, and songbirds also utilize the Central Valley wetlands. The total annual waterbird count (including migrants) in the region has been estimated as high as 10 to 12 million (Gilmer et al. 1982).
With the gradual loss of wetlands in the Central Valley, wildlife has become increasingly dependent on agricultural lands for food and cover. While most agricultural development is deleterious to wildlife, the agricultural wetlands created by rice cultivation have provided an important mitigation for the extensive loss of natural wetland habitats. Although rice culture habitats are not as ecologically productive as natural wetlands, they are a viable alternative, and vastly superior to other agricultural options or urban development. Rice fields are typically flooded for about five months a year during which time they become temporal wetlands with enormous significance to bird populations wintering and breeding in the Central Valley. Since 60 percent of all the waterfowl on the Pacific Flyway winter in the Central Valley, both natural and agricultural wetlands are indispensable to them. Flooded rice fields are also vital to migrant and wintering shorebirds. Some 230,000 shorebirds winter annually in the Central Valley and, during fall migration, their numbers can swell to over 400,000 (Shuford et al. 1993; Page et al. 1994). Rice fields provide feeding habitat for nearly 70 percent of these migrant shorebirds during their journey south (Page et al. 1994). Without rice farming, wetland habitats in the Central Valley would be reduced by as much as 45 percent. A loss of this magnitude would have a disastrous effect on waterfowl, and a host of other wetland-dependent species. Equally important, the waste grain left after the rice harvest is a major source of food for a number of waterfowl species. The rice farmers also benefit by receiving large amounts of natural fertilizer left behind in the droppings of these feeding flocks.
For a variety of reasons that include loss of wetlands, extended periods of drought on the breeding grounds, loss of nesting habitat, the waterfowl wintering in California has declined dramatically since the late 1970s. Through the efforts of waterfowl conservation groups, and the proactive management of both breeding and winter waterfowl habitats by the federal government, the decline in California's waterfowl population began to change and started to increase in the late 1980s. If this trend continues as expected, more wetlands in the Central Valley will be needed to accommodate this increase. The most viable source of new wetlands lies in sustained collaborative efforts to promote the post-harvest flooding of rice fields through the winter.
At least 30 special status wildlife species (27 birds, 2 reptiles, and 1 amphibian) listed by the state of California or the federal government as endangered, threatened, candidate species or species of special concern, are known to utilize flooded rice fields, fallow rice fields, or recently drained or harvested rice fields during their annual cycle (Table 2-1). Of these species, seven are known to breed in, or are in some way dependent on, rice culture habitats for successful reproduction. Their status and relationships to habitats associated with rice farming are summarized below.
Collectively, including the special status species, 141 species of birds, 28 species of mammals, and 24 species of amphibians and reptiles are known to utilize rice culture habitats in California (see Appendix A for species lists).
Table 2-1:
Special Status Wildlife Species Known to Utilize
Rice Culture
Habitats During Their Annual Cycle
| Species | Scientific Name | Status |
| AMPHIBIANS | ||
| Western Spadefoot | Scaphiopus hammondii | CSC |
| REPTILES | ||
| Western Pond Turtle | Clemmys marmorata | CSC |
| Giant Garter Snake* | Thamnophis gigas | ST, FT |
| BIRDS | ||
| Double-crested Cormorant | Phalacrocorax auritus | CSC |
| American Bittern* | Botaurus lentiginosus | FSC |
| Great Egret | Casmerodius albus | CSC |
| Snowy Egret | Egretta thula | CSC |
| White-faced Ibis | Plegadis chihi | CSC |
| Aleutian Canada Goose | Branta canadensis leucopareia | FT |
| White-tailed Kite | Elanus leucurus | SP, FSC |
| Bald Eagle | Haliaeetus leucocephalus | SE, FE |
| Northern Harrier* | Circus cyaneus | CSC |
| Swainson's Hawk | Buteo swainsoni | ST |
| Ferruginous Hawk | Buteo regalis | CSC |
| Golden Eagle | Aquila chrysaetos | CSC |
| Merlin | Falco columbarius | CSC |
| Peregrine Falcon | Falco peregrinus | SE, FE |
| Prairie Falcon | Falco mexicanus | CSC |
| Greater Sandhill Crane | Grus canadensis tabida | ST |
| Mountain Plover | Charadrius montanus | CSC, FSC |
| Long-billed Curlew | Numenius americanus | CSC |
| Black Tern* | Chlidonias niger | CSC |
| Burrowing Owl* | Speotyto cunicularia | CSC |
| Long-eared Owl | Asio otus | CSC |
| Short-eared Owl* | Asio flammeus | CSC |
| Bank Swallow | Riparia riparia | ST |
| Bewick's Wren | Thryomanes bewickii | FSC |
| Loggerhead Shrike | Lanius ludovicianus | CSC |
| Lark Sparrow | Chondestes grammacus | FSC |
| Tricolored Blackbird* | Agelaius tricolor | CSC |
Status Codes
CSC: California Department of Fish and Game "species of special concern".
FE: Listed as endangered by the Federal Government.
FT: Listed as threatened by the Federal Government.
FSC: Federal species of management concern (see Trapp 1995)
SE: Listed as endangered by the State of California.
SP: Listed as protected by the State of California.
ST: Listed as threatened by the State of California
* Species breeds or is in some manner dependent on rice culture habitats for successful reproduction.
Note: Federal Government dropped all numbered designations of "Category Candidate" species in 1996 (FR February 28, 1996, 61:7595-7613). The former Category 1 candidates species are now the only "Candidate" species considered by the U. S. Fish and Wildlife Service.
AMPHIBIANS
Western Spadefoot (Scaphiopus hammondii): Spadefoot toads are adapted to breeding in temporal supplies of water, such as vernal pools, which allow them to deposit their eggs and mature before the ponds dry up. The toads are active at night and spend most of the year in underground burrows emerging during periods of heavy rainfall to begin breeding (Morey 1988). Western spadefoot toads are occasionally found in drainage ditches and on check levees surrounding rice fields (G. Hansen per. comm. 1994).
REPTILES
Western Pond Turtle (Clemmys marmorata): This species is usually found along the quiet waters of marshes, streams, and ponds where it feeds upon aquatic plants, fish, crayfish, invertebrates, and carrion (Stebbins 1972; Bury and Holland 1994). Habitat destruction, exotic predators, and water diversions are commonly cited reasons for the decline of this species. Turtles are frequently found basking along levees and drainage ditches bordering flooded rice fields where they feed on fish and invertebrates. Rice fields are becoming an increasingly important habitat for pond turtles (G. Hansen et al. 1992).
Giant Garter Snake (Thamnophis gigas): The giant garter snake was found originally in the Central Valley from Sacramento to Buena Vista Lake near Bakersfield (Fitch 1940). It is a wetland-adapted snake that was common near lakes and rivers on the riparian flood plain of the Central Valley. By 1971, the loss of wetland habitat, coupled with agricultural practices such as tilling, grading, burning, harvesting, weed abatement, and grazing, eliminated the giant garter snake from the southern San Joaquin Valley (Ellis 1988). The present distribution consists of 13 disjunct populations from just south of Chico to Stockton (Sorenson 1993). Introduced predators such as bass (Micropterus sp.), sun fish (Lepomis sp.), and catfish (Ictalurus sp.) have limited the range of habitat available to giant garter snakes by narrowing corridors of dispersal, and forcing them into warmer waters and ephemeral seasonal wetlands. While most of the native habitat has been lost for this species, some populations have been discovered utilizing irrigation canals, check levees, and rice fields in the American and Butte Basins (Hansen 1986). Flooded rice fields have become such an important alternative habitat that, without them, the species would be at serious risk of extinction (G. Hansen pers. comm. 1994). The phased-reduction of burning rice fields mandated by the state legislature by 1998 will have some beneficial effect on the giant garter snake by providing additional escape cover, and reducing their exposure to predators. Habitat degradation and fragmentation continues to compromise existing populations.
BIRDS
Double-crested Cormorant (Phalacrocorax auritus): Significant declines in double-crested cormorant populations in a number of states through the late 1930s (Palmer 1962) prompted a concern for the remaining populations (Ehrlich, Dobkin and Wheye 1992). The loss of suitable nesting habitat, disturbance, over-fishing, pesticides, and pollutants are the most frequently cited causes of the historical declines (Remsen 1978; Harvey et al. 1992). In several areas of California, however, they now appear to be more common than they were 30 years ago (Shuford et al. 1989). Double-crested cormorant numbers have increased along the coast since the 1980s (Harvey et al. 1992) and, although their populations in the Central Valley are not as well understood (H. Carter pers. comm. 1994), they are believed to be increasing there as well (E. Beedy pers. comm. 1994).
Double-crested cormorants are often seen foraging for fish on reservoirs, rivers, and ponds, but will occasionally utilize flooded rice fields when conditions are right. They also use check levees to dry their wings after feeding in the deeper waterways that sometimes border rice fields.
American Bittern (Boturus letiginosus) is a species more typically associated with cattail and bulrush dominated marshes, but they will also nest in tall grass near marshes (Palmer 1962). American bittern populations are currently declining at a rate of approximately 1.6 percent per year since the mid-1960s (Peterjohn and Sauer 1993), most likely as a result of the loss of suitable wetland habitats. They feed on a wide variety of food that includes tadpoles, insects, small fish, reptiles, frogs, and crayfish (Palmer 1962), the latter of which are common in flooded rice fields and irrigation ditches. While they prefer to remain concealed in dense marsh vegetation, bitterns are occasionally seen feeding, often at dusk, in flooded rice habitats and rice irrigation ditches.
Great Egret (Casmerodius albus) and Snowy Egret (Egretta thula): Plume hunters nearly drove great and snowy egrets to extinction in the late 19th Century until the demand for their plumes fell out of fashion in the millinery trade. Their conspicuousness and habit of breeding in colonies made them easy targets. By the 1940s, egret numbers had recovered over most of their range in California (Grinnell and Miller 1944) and, although current populations seem stable enough (see Shuford 1993), both species are very vulnerable to disturbance around the nesting colonies. They continue to suffer the loss of suitable nest sites to development.
Great and snowy egrets utilize a wide variety of aquatic habitats. They are often seen foraging for fish, crayfish, amphibians, reptiles, and arthropods in flooded rice fields during the nesting season, and bringing back their catch to the nesting colonies to feed their young.
White-faced Ibis (Plegadis chihi): The white-faced ibis was once a common breeding species throughout much of California. Declines in the California populations were noticed in the early 1940s (Grinnell and Miller 1944), and the species appeared to be in serious trouble by the 1960s. The primary factors implicated in this decline have been habitat destruction and pesticides (Henny and Herron 1989). Since 1980 a population surge has been observed over much of its former California range. The species is now nesting in the Colusa and Gray Lodge Refuges, where breeding has not occurred for more than 25 years. Flocks of 1,000 birds have been observed in the Butte Sink during the winter (B. Deuel pers. comm 1991), and Sacramento Valley counts of white-faced ibis for the periods of November and January, 1992-93 to 1994-95, ranged from 763 to 3,120 birds (Shuford and Hickey 1996). Numbers of this magnitude are unprecedented in more than 50 years. By comparison, fewer than 200 birds were found in the entire state during the winter of 1976-77 (Remsen 1978). This surge in California's wintering population of white-faced ibis is likely the result of a westward shift in the breeding populations from the Great Basin promoted by flooding and habitat loss, plus improved breeding habitat conditions in Oregon and northern California (Henny pers. comm. 1991; Shuford and Hickey 1996).
In recent years, a number of observers have noted that white-faced ibises actively feed in flooded rice fields (E. Beedy; D. Whitmore; T. Manolis; B. Duel, pers. comm. 1991; 1997). Five winter surveys (1992-93 to 1994-95) of the Sacramento Valley found 66 percent of the ibis concentrated in agricultural fields, of which rice stubble was the single most important habitat as it held an average of 53 percent of the foraging ibis observed (Shuford and Hickey 1996). Further research is needed on both the changing status of this species, and its ecological requirements in California. Rice fields appear to be an important alternative to natural white-faced ibis habitat in the Central Valley.
Aleutian Canada Goose (Branta canadensis leucopareia): The Aleutian canada goose, a small subspecies of Canada goose, nests exclusively on the Aleutian Islands in Alaska. Introduced predators on its nesting grounds reduced the population to less than 800 birds by 1975 (Amaral 1985). With efforts to control introduced foxes that are preying on its nesting grounds, the population has rebounded to a total of about 22,000 birds (pers. comm. P. Springer and M. Fisher 1997). The entire population winters in northwestern and central California. About 3,500 of these birds were regularly observed feeding on waste corn and rice in the Colusa Basin in the fall and winter of 1986 and 1987 (Gregg, Eckhardt and Springer 1988). Unharvested grain forms an important part of this species' diet during their migration.
White-tailed Kite (Elanus leucurus): This species suffered a serious decline in California during the first half of the century from indiscriminate shooting, egg collecting, and habitat loss (Waian and Stendall 1970). it was believed to be going extinct in the state by the mid-1920s (Pierce 1928). It was given fully protected status by the California legislature in 1957, and since that time their numbers have steadily increased. Concern for their populations is still an issue in several areas of the west coast (Trapp 1995). However, their numbers in California now appear to be fairly stable but are subject to fluctuations in their prey populations, and this effects their reproduction (Pruett-Jones et al. 1980). White-tailed kites are often seen foraging over dry rice fields in late winter after the draw down, during flood up when rodents are driven out of the fields, or in fallow rice fields where they hunt for small rodents (often catching house mice), large insects, and an occasional snake or frog.
Bald Eagle (Haliaeetus leucocephalus): The bald eagle population declined steadily during the first half of the twentieth century for a variety of reasons that include the effects of pesticides, habitat loss, accidents, shooting, bounty hunting, and poisoning (Johnsgard 1990; Green 1985). The population low occurred in 1963 when only 417 pairs were known in the lower 48 states (Miller 1994). Coupled with the protection extended to it by the Endangered Species Act, bald eagles have been increasing steadily since 1972 when a nationwide ban on DDT helped reduce eggshell thinning and improved reproductive success (Jurek 1988; Palmer 1988). By 1993 there were more than 4,000 pairs in the lower 48 states. The U.S. Fish and Wildlife Service (USFWS) recently reached a determination that the bald eagle had recovered sufficiently to reclassify from an endangered to a threatened species throughout most of the country (Miller 1994). The success of the bald eagle comeback is a good example of how endangered species legislation was intended to work. Bald eagles occasionally forage over flooded rice fields in winter looking for crippled ducks and geese, and taking fish when available.
Swainson's Hawk (Buteo swainsoni): The Swainson's hawk, once an abundant breeding species over most of the state, is now threatened with extinction in California because of the loss of both foraging and nesting habitats. Estimates of the historical population in California range as high was 17,000 breeding pairs, but the current population stands at only 550 breeding pairs (California Department of Fish and Game [CDFG] 1993).
Swainson's hawks nest almost exclusively in riparian habitats along major river courses, selecting large trees with a commanding view of the surrounding countryside. Ancestral populations of Swainson's hawks foraged for small mammals over the expansive native grasslands that were once prevalent in California. Much of this habitat has now been urbanized or converted to agricultural. However, this species has adapted to using certain agricultural crops as foraging habitat with a good deal of success. A recent study conducted in the Central Valley indicated that fallow rice fields, (which would include fallow rice fields) and recently disked fields, were highly preferred foraging habitats harboring substantial prey populations (Estep 1989). Although agricultural habitats are not a desirable substitute for natural grasslands, the biggest current threat to the existence of this species in California is the ongoing urbanization of the Central Valley.
Ferruginous Hawk (Buteo regalis): At the northern limit of the species' range in Saskatchewan and Alberta, Canada, it is estimated that its breeding distribution has declined by 60 percent (Schmutz 1985). However, recent data suggests that their numbers may be increasing in California (Garrison 1990). Ferruginous hawks breed in small numbers in northeastern California, but they occur primarily during winter when they are often seen foraging over fallow rice fields in search of jackrabbits and ground squirrels.
Golden Eagle (Aguila chrysaetos): Concern for possible declines in golden eagle breeding populations in the 1970s (Remsen 1978) resulted in the CDFG placing it on the species of special concern list. Golden eagle numbers now appear to be fairly stable over most of the state, but because they have large home ranges they often come in close contact with ongoing development. They are very sensitive and generally intolerant to disturbance around their nests. Golden eagles breed in the foothills surrounding the Central Valley (and in the Sutter Buttes) and are seen foraging over large areas (including rice fields) in search of food.
Merlin (Falco columbarius): The merlin is a winter visitor to California. Suspected population declines (Fox 1964; 1971) prompted concern by various agencies 25 years ago (Remsen 1978), but most biologists now feel that merlin populations are doing well (see Palmer 1988; Johnsgard 1990). Merlins are regularly seen during the winter darting across flooded rice fields hunting songbirds and shorebirds.
Peregrine Falcon (Falco peregrinus): Prior to World War II, peregrine falcons nested throughout much of California. They were found from sea level to over 7,000 feet, with the densest populations along the coast, in the Cascades, and in the Sierra Nevada (Jurek 1989). Beginning the 1940s, the widespread use of chlorinated hydrocarbon pesticides, such as DDT, triggered a precipitous decline in peregrine populations throughout North America and in much of the rest of the world. These pesticides concentrate in the tissues of prey populations and are subsequently passed to the peregrines themselves resulting in the inability of the females to form normal eggs. By the late 1960s, the species was seriously threatened over much of its range. Recovery efforts over the past 20 years have brought the breeding population in California from less than 10 active sites in 1975 to over 130 in 1994 (B. Walton pers. comm. 1994). Pesticides still plague nesting peregrines in California in spite of a ban on DDT since 1972 (Risebrough and Monk 1989), but the recovery of this species in California and across North America is encouraging and a testament to the effectiveness of the Endangered Species Act (ESA). Peregrine falcons winter in the Central Valley where they take long foraging flights over the surrounding wetlands and flooded rice fields, hunting for ducks and shorebirds.
Prairie Falcon (Falco mexicanus): Prairie falcons are present in the Central Valley all year and they probably breed in the Sutter Buttes. The breeding population in California has been estimated at about 250 to 300 pairs (B. Walton pers. comm. 1994) with more than 500 possible breeding territories available (Boyce, Garrett and Walton 1986). The winter population can reach 1,200 birds (Johnsgard 1990). The species has disappeared in some regions of the state because of the loss of habitat. Prairie falcons are occasionally seen foraging over fallow and flooded rice fields, usually during the winter.
Greater Sandhill Crane (Grus canadensis tabida): The California population of the greater sandhill crane breeds in small numbers (circa 170 birds) in the northeastern part of the state (Littlefield 1989) and joins a larger population of about 6,400 birds that winter in the Central Valley and the Sacramento Delta (Pogson 1990). There are five greater sandhill crane populations presently recognized, but the Central Valley populations the only one believed to be declining on its breeding grounds (Littlefield 1989). The breeding populations in California have made only modest gains, while populations in Oregon have declined significantly.
More than half the Central Valley population of this species occurs in the butte Sink during November and December, taking advantage of the waste grain left after the harvest. Harvested rice fields are the most important feeding areas in the Sacramento Valley and provide much needed carbohydrates in the diet of the cranes. The check levees, borders of the rice fields, and irrigation ditches also provide additional feeding areas, while flooded rice fields provide nocturnal roost sites (Pogson 1990).
Mountain Plover (Charadrius montanus): The mountain plover is a highly specialized and local species that breeds in shortgrass prairie habitats of the Great Plains. it winters mainly in Texas, Arizona, and in northern Mexico, but a small number winter in the Central Valley (mostly in the San Joaquin Valley) of California. Recent estimates indicate that mountain plover populations have declined by some 63 percent since 1966. (Knopf and Miller 1994). Early declines were associated with over hunting, but the continued conversion of shortgrass prairie habitat to agriculture in this century is believed to be the major factor limiting their population today (Ehrlich et al. 1992).
Mountain plovers only occur sporadically and are very local along the southern edge of the major rice growing areas of Sacramento Valley. They are sometimes seen in late winter in recently disked rice fields where they feed on insects and other invertebrates brought to the surface by tillage.
Long-billed Curlew (Numenius americanus): This species breeds in small numbers in the northeastern part of the state, but is present all year in the Central Valley where a few non-breeding birds are present in summer. Long-billed curlew breeding populations have declined over much of their range, particularly in the east-central United States (Johnsgard 1990). This species is frequently seen foraging in flooded rice fields, particularly in fall and winter, where they probe for invertebrates.
Black Tern (Chlidonias niger): the black tern once bred throughout most of California, preferring freshwater marshes, ponds, and emergent wetlands for nesting (Grinnell and Miller 1944; Beedy 1985). The loss of wetlands necessary for breeding and feeding has reduced this species to a few isolated colonies in the Central Valley where it was once common. The remaining black tern colonies have adapted to breeding in flooded rice fields. Without rice fields the black tern would be virtually eliminated as a breeding species in the Sacramento Valley.
Short-eared owl (Asio flammeus) and Northern Harrier (Circus cyaneus): These two species of raptors were widespread inhabitants of California's grasslands and are ecological counterparts of one another; one hunts for small mammals during the day and the other hunts the same areas at night. Neither species is as common as it once was in California and, in some areas, significant population declines date as far back as the 1900s (Tyler 1913). Grazing, agricultural, and urban development of nesting habitats, and shooting have contributed to reduced populations. Rice set-side fields, particularly those out of production for several years, are used frequently by harriers and short-eared owls for breeding. In a recent waterfowl nesting survey in the Sacramento Valley, Loughman and Yarris (1990) found 16 northern harrier nests and three short-eared owl nests in 861 acres of fallow rice fields. Flooded rice fields would hold little interest for either species, but their response to other agricultural habitats, such as disked and fallow rice fields, is probably quite similar to Swainson's hawks; i.e., these habitats can be exploited favorably when prey abundance permits.
Long-eared Owl (Asio otus): The long-eared owl is a poorly known species in California, but available evidence indicates it has disappeared from many areas of the state (Remsen 1978). It no longer breeds regularly in the Central Valley where it would forage over open grasslands from its riparian nesting areas. Much of its foraging habitat has been converted to agricultural lands. However, long-eared owls are occasionally found roosting in trees bordering rice fields and probably forage over fallow rice fields at night.
Burrowing Owl (Speotyto cunicularia): This species was widespread in California prior to 1945 (Grinnell and Miller 1944), but urbanization and agricultural conversion of nesting areas has reduced the population significantly since the end of World War II. Existing populations have been reduced to small fragmented groups frequently surrounded by urban development. A recent study estimated that a decrease of nearly 60 percent in the California burrowing owl populations has occurred since the 1980s (DeSante and Ruhlen 1995). Burrow destruction, the effects of grazing, shooting, secondary poisoning from ground squirrel eradication programs, and collisions with automobiles have historically been the most frequently cited factors for their decline (Remsen 1978). However, in the past 20 to 30 years the phenomenal increase in commercial and residential development has produced the largest single impact on their population. The CDFG considers it a species of special concern, but current research (DeSante and Ruhlen 1995) could justify placing the burrowing owl on the state endangered or threatened species list. Burrowing owls are occasionally seen nesting in the check levees that border the rice fields where they feed on small rodents and arthropods.
Bank Swallow (Riparia riparia): The bank swallow was once a common widespread species in California. The species no longer breeds in southern California, and only a few colonies remain on the coast. Its breeding range in California has decreased by 50 percent (Laymon et al. 1988). Bank swallows nest by constructing burrows in soft loam soils, usually along river and streambanks. Because of extensive erosion control, bank stabilization and riprapping programs, many nesting colonies along river banks have been destroyed. The Sacramento and Feather Rivers harbor 75 percent of the remaining breeding populations in the state, and yet even these colonies continue to be threatened by riverbank stabilization programs (Garrison et al. 1987). The Sacramento River populations have declined by 44 percent since 1986 (Schlorff 1997). This species is often seen foraging for insects over flooded rice fields during the spring and summer months.
Bewick's Wren (Thryomanes bewickii): Recent declines in Bewick's wren populations have prompted concern for this species in regions of the far west (Peterjohn and Sauer 1993). They have been declining in the eastern and central regions of the country since the mid-1960s (Robbins et al. 1986). However, the populations in California appear fairly stable. Bewick's wrens are occasionally seen in fall and winter foraging for insects in weedy ditches bordering rice fields in fallow rice fields.
Loggerhead Shrike (Lanius ludovicianus): Loggerhead shrikes are often seen hunting from small trees bordering rice fields, and in fallow rice fields. The populations in California are fairly stable; however, the species is declining over much of its North American range. Habitat loss and pesticides are cited as the major factors in this decline (Morrison 1981; Fraser and Luukkonen 1986).
Lark Sparrow (Chondestes grammacus): Although lark sparrows are still fairly common across most of their range, recent estimates indicate that they are declining at a rate of 3.4 percent of their population per year (Peterjohn and Sauer 1993). If this estimate is at all accurate, it will not be long before a significant segment of their population disappears.
In California they are mostly a resident species preferring grassland dominated habitats where they place their nests on the ground or in a small shrub (Markle 1946). They are often seen feeding along roadsides or singing from fence lines. Lark Sparrows are casual visitors to rice habitats, occurring mostly in the fall and winter, where they are sometimes found feeding along weedy irrigation ditches, or in fallow rice fields.
Tricolored Blackbird (Agelaius tricolor): Blackbirds associated with rice cultivation have traditionally been considered pests that are capable of damaging rice crops during the milk and dough stages of development. As the rice industry grew so did the damage because blackbirds are adaptable and would turn to eating rice when natural foods became scarce. However, with rapidly maturing rice varieties, and the use of repellent devices such as gas cannons and AV alarms, the damage has been reduced to tolerable levels.
Virtually, the entire world population of tricolored blackbirds is restricted to California (Neff 1937). Once, it was an abundant breeding species with most of the population located in the Central Valley where its primary nesting habitat is cattail and tule marshes (DeHaven et al. 1975). It has been suggested that this species benefitted by rice production (Orians 1961), but as rice acreage grew after World War II, tricolored blackbirds began to decrease. No one knows the size of the ancestral population, but it was surely in the millions. By the early 1970s, DeHaven and Crase (1974) felt that the populations were perhaps 50 percent of what they were in the 1930s. A recent study indicates that the population may have further decreased (Beedy et al. 1991). Because of their erratic nesting behavior tricolored blackbirds are difficult to census, but the best current estimate of the California population is 250,000 to 300,000 birds (W. Hamilton pers. comm. 1997). The loss of marsh nesting habitats, toxics, predators, and possibly pesticides are thought to be the primary reasons for the decline of this species. Concern for existing populations is justified because the species is highly colonial and vulnerable to large population losses resulting from a single impact.
Crase and DeHaven (1978) reported that rice constituted about 38 percent of the annual diet of the tricolored blackbird. However, they also consume watergrass (18 percent), and smartweed (1 percent) and 39 percent of the food they feed their young are rice weevils (Crase and DeHaven 1977), all of which are harmful rice crop pests. Consequently, there is some mutually beneficial resource exchange between the rice grower and the tricolored blackbird.
