Along with the Sierra Nevada, the Central Valley is one of the West's mostrecognizable geological features. Spanning 400 miles, the Valley was formed byintermittent alluvial deposition events. The Central Valley's vegetationcommunities were shaped by a complex hydrology, mild climate, and isolation bythe Sierra Nevada. These conditions provided a variety of niches that have ledto a diverse avifauna (bird diversity). The ornithological, scientificcommunity recognizes the Central Valley as one of the continent's most diverseinland regions, in terms of both species richness and total number of birds.The key to this avian diversity is the Valley's hydrology.
Much of the state's water supply is carried by two river systems, theSacramento and San Joaquin, fed by melted snow from the Sierra Nevada. Theestimated mean seasonal runoff of all California rivers is 71 million acrefeet. The Sacramento River provides 35% of this flow and the San Joaquin Riverprovides about 25% of this total. The remaining flow is supported by therivers of the Coast Range. Most of the Central Valley rivers are now dammedand water is routed to more arid regions of the state for urban, industrial,and agricultural uses. Despite the flood control protection provided by thesedams, the Central Valley continues to experience massive flood events. Theseevents are most likely to follow warm winter storms that cause a premature meltof Sierran snows. Floods typically occur from January through March, duringwhich times, the Valley's rivers can experience peak flows exceeding 60 millionacre-feet (in 1906-07, 63.3 million acre-feet was recorded).
The Sacramento River drains the northern third of the Central Valley and is thelarger of the two systems. Major tributaries include the Feather, American,and Bear rivers. The Butte Basin, Sutter Buttes, and riparian forests of theupper Sacramento River provide important habitat for birds in the Valley. TheSan Joaquin River drains the central third of the Central Valley. Majortributaries include the Mokelumne, Stanislaus, Tuolemne, and Merced rivers.The southern San Joaquin Valley has a distinct hydrology dominated by aterminal sink, the Tulare Basin, fed by the King and Kern rivers. The TulareBasin was created by late subsidence and, prior to instream diversions,supported two intermittent lakes, Tulare and Buena Vista. These lakessupported great concentrations of wildlife.
The Central Valley historically supported three major landscapes: wetlands,grassland-prairies, and riparian (riverside) woodlands. These habitats wereall hydrologically and biologically linked to the river systems. Wet, mildwinters and long, hot summers helped create the vegetation communities thatcharacterize the Central Valley. Prior to dams, the major rivers meandered,forming oxbows and riparian habitat. Winter floods would inundate and scourareas along these rivers, creating marshes and early succession riparian scrub.Plants needed to be adapted to survive the flood conditions, in addition tolong, hot summers and periods of drought.
Many scientists recognize California as a unique biological region of theworld. This California realm is characterized by a Mediterranean climate,geologic isolation by the Sierra Nevada and Cascade Mountains, a high number ofendemic (found no where else) species of plants and animals, and a uniqueassemblage of vegetation communities. Although the Central Valley is mostrecognized for its fantastic waterfowl, raptor, and other wildlifeconcentrations, it is in the xeric (dry) oak woodlands, chaparral, and oaksavannah habitats that one finds the avifauna component that helps define theornithologically significant California realm. This avifauna componentincludes: white-tailed kite, California quail, Anna's hummingbird, Nuttall'swoodpecker, plain titmouse, bushtit, yellow-billed magpie, scrub jay,California thrasher, wrentit, California towhee, and Lawrence's goldfinch.Most of these species are unique to California and still live in the CentralValley.
Prior to the European settlement of California, the state's wetlands coverednearly five million acres. As we move into the last decade of the twentiethcentury, only 5% of the 5 million acres remain. For example, theSacramento-San Joaquin Delta (Delta) historically supported 500 square miles oftidal freshwater marsh, most of which was concentrated in the southern andeastern Delta. The northern Delta, once a complex of river systems andseasonal basins dominated by the Sacramento, Mokelumne, and Cosumnes rivers,historically flooded during winter. Thousands of acres became inundated duringrainy periods and portions of the region essentially became an inland lake.Also, characteristic of the northern Delta were luxuriant stands of riparianforests dominated by valley oak, Fremont cottonwood, and several species ofwillow. Canopy trees are characteristically tall and diverse, multi-layeredcanopy, draped with lianas, were reminiscent of tropical lowland forests.These vast tracts of seasonal and permanent wetlands and riparian forests inthe northern Delta supported a rich variety of wildlife dominated by hundredsof thousands of waterfowl. Grizzly bear, tule elk, many species of smallermammals, and millions of other birds also occurred here.
The massive undertaking to reclaim land in the Delta, to exploit rich alluvialsoils for agriculture, began before 1900. Flood control levees, waterdiversion canals, and dams in the watershed rerouted water to the San JoaquinValley and southern California. Controlled waterflow forever changed thehydrology of the Delta and, today, has resulted in concerns for inlandfisheries and water quality. The riparian forests, cleared for agriculture andhardwood needs, rapidly diminished because of channelization of the region'srivers.
Other regions have been equally modified, essentially redefining the hydrologyof the entire Central Valley. Today, protection and restoration of theremaining resources are the primary goals of many private and public wildlifeconservation organizations. However, the private landowner can, and continuesto, make the difference in providing habitat for wildlife. Only throughprivate land and public agency cooperation can we hope to maintain thediversity of birdlife in the Valley.
The Central Valley supports nearly 250 species of birds. This vast resourcecan be characterized into four groups based on annual occurrences: residents,winter visitors, summer visitors, and transients. These seasonal patterns ofbird movement in the Central Valley are important to understand for plannedrestoration and wildlife-friendly farm management activities.
The avifauna of the Central Valley is discussed in two parts. Part I treatsthe breeding avifauna of the Central Valley focusing on the permanent andsummer residents and includes short treatment on threatened and endangeredbirds. Part II focuses on the winter residents and transient birds that visitthe Central Valley. The majority of these species are waterbirds that exploitthe restored and managed wetlands and agricultural resources.
The Central Valley's breeding avifauna is defined by those birds that areyear-round residents and those that spend the summer months in the Valley.Several summer species have declined in recent decades due to a variety ofreasons, including habitat loss and pesticide use. Many of these decliningspecies are now federal and state recognized as rare and threatened and havebecome a particular concern for the private landowner.
Permanent residents are those species which contain populations that spendtheir entire annual life cycle in the Central Valley. Examples are:California thrasher, scrub jay, mallard, great blue heron, wood duck,white-tailed kite, killdeer, Nuttall's woodpecker, and rufous-sided towhee.Ninety-two species of permanent resident birds occur in the Valley (Appendix).Some species are only resident in portions of the Valley. For example,white-faced ibis and American avocet are resident in the San Joaquin Valley butare summer visitors in the Sacramento Valley. The resident birds in your areashould be a subset to the total list provided in the Appendix.
Many of our resident species are considered generalists, exploiting a varietyof food sources and habitats, and are common throughout the Central Valley inthe natural habitats that support them. Some have adapted to conversion ofnatural habitats to agricultural lands and urban settings, while others havedeclined. During the past 100 years, agricultural lands have become anintegral component of land use for several species of residents. Open spacesettings of agricultural fields, in association with wind break plantingsaround farm houses, provide habitat for red-tailed hawk, American kestrel, barnowl, and yellow-billed magpie. Pastures provide hunting habitats for heronsand raptors. The creation of stock ponds has created opportunities for mallardand pied-billed grebe. Simple modifications or more elaborate habitatrestoration projects on farms can benefit the target species, but can alsoserve to increase bird diversity on a site. For example, allowing a portion ofa stock pond to grow emergent vegetation can improve habitat for mallards andgrebes, and also provide nesting opportunities for moorhens, blackbirds, andmarsh wrens.
Numerous species of waterfowl breed in the Central Valley, but four species arewidespread residents. The mallard is the most common breeding species foundthroughout the Valley. It prefers marshes, ponds, lakes, and irrigationditches, and requires uplands within one mile of their permanent water body.Cinnamon teal and gadwall are also common, breeding in semipermanent andpermanent marshes, ditches, and small ponds. Both breed closer to water thando mallards. The wood duck is the fourth species. Wood ducks nest in treecavities near permanent rivers, ponds, and lakes. Many landowners and wildlifeareas place artificial nest-boxes for wood ducks. Wood ducks are most commonin the Delta and Sacramento Valley.
A melodious song reminiscent of a mockingbird may at times be the onlyindication that a California thrasher is present in the dense riparian scruband chaparral it inhabits. A non-migratory species, California thrashers wereonce abundant on the Valley floor but habitat loss (riparian scrub) hasresulted in the species decline. California thrashers are still common inchapparal of the foothills.
Two-thirds of its foraging is accomplished on the ground, where they feedprimarily on large insects. Some studies have shown a preponderance forforaging on terrestrial nesting wasps. During fall, California thrashers willseek fruits of toyon and other shrubs. California thrashers form a pair bondthat lasts throughout the year. The pairs do not associate with otherthrashers and, after broods are grown, form small family groups. They are,however, aggressive to other species.
California thrashers are well adapted for terrestrial life, possessing long,powerful legs and a long, decurved bill that allows them to probe beneathdetritus. Foraging is often active, with the birds scratching debris withtheir feet, and probing in soils with their bill. They are a terrestrial bird,running swiftly on the ground and infrequently flying. A recluse, this bird israrely seen in the open and does not cross wide openings between habitatpatches. As such, it is frequently referred to as a shy bird. Although itsprimary habitat is rather deficient of water, California thrashers do make useof standing pools and streams of water. Dispersal during winter into adjacentriparian habitats has been documented.
Summer residents breed in the Central Valley in summer and migrate to southernclimates for winter (Fig. 1). Many of these species are called neotropicalmigrants because they winter in Central and South America (the neotropics -[new world tropical region]). Examples of summer visitors include: cinnamonteal, Swainson's hawk, American avocet, western kingbird, blue grosbeak, andnorthern oriole. The Central Valley supports 39 species of summer residents(Appendix).
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Figure 1.
As with winter migration, there are several temporal patterns for summerresidents. Cinnamon teal and yellow-headed blackbird, for example,predominantly migrate to southern California and northern Mexico and return tonest in the Valley. The shortest haul belongs to some populations of theAmerican avocet, which nest in the Valley, and winter in San Francisco Bay andin other California estuaries. Many of our forest birds winter much farthersouth in Central and South America. These migrations are indeed amazing asthese forest birds must traverse large bodies of water, desert climates, andmountain ranges. One of the long distance champions is the Swainson's hawk,which breeds in the Central Valley. Their migration route takes them south tospend winter months in Patagonia, Argentina; a migration of 8,000 miles oneway!
Summer residents begin to arrive in the Central Valley by mid-February toestablish nesting territories. Cliff, tree, and rough-winged swallows arrivefirst, followed by western kingbirds, which become numerous by mid-March. ByApril, northern orioles, black-headed grosbeaks, ash-throated flycatchers, andothers become numerous. A second wave of species arrive in May, these includelate nesting birds such as blue grosbeaks, lazuli buntings, and western woodpewees. Blue grosbeaks are still establishing territories into mid-June. Themarsh dwellers begin to arrive by mid-march. They are met by already nestingresident species. Late spring arrivals include yellow-headed blackbird, leastbittern, and black tern. By mid-summer, the number of bird species residing inthe Valley totals 131 (permanent residents plus summer residents).
Some summer residents are very local in the Valley. Summer tanagers forexample nest only in the southern San Joaquin Valley (Kern County).Yellow-billed cuckoos, a state endangered species, are restricted to riparianwoodlands of the northern Sacramento Valley, and the Kern River. Leastbitterns can only be found in dense tule patches and semi-permanent marshes offederal and state wildlife areas and private duck clubs.
In California, this buteo (hawk) is a summer resident in the Great Basin,Central Valley and along the south coast. It is widespread throughout westernNorth America (Fig. 1). Estimates place the state population at 375 birds,down from historical estimates that range from 4,200 to 17,100 birds. A numberof factors have been suggested to explain the decline of the species inCalifornia. Mortality during migration, pesticide poisoning in the breedingand wintering grounds, egg shell thinning, habitat loss, disturbance,degradation of habitat, and increased competition with other species ofraptors. No single factor provides an adequate explanation for the observeddeclines in California.
Swainson's hawks migrate through the Pacific and Central flyways to grasslandregions of South America (Fig. 1). In the Central Valley, the birds generallyreturn to breeding sites by mid-March and migrate in fall from Septemberthrough mid-October. Birds nesting in Western Canada and states north ofCalifornia migrate through the Central Valley.
Swainson's hawks nest almost exclusively in trees, with a few recorded on clifffaces and on the ground. Nesting trees are typically located on the edgesbetween woodlands and either grasslands or shrub habitats, or in isolated treesand clumps in open country. In most cases, the tree selected is the largest inthe area, and the nest has a panoramic view.
The Swainson's hawk is an aerial predator in open country. Soaring on updraftsor relatively high coursing are common tactics used by the species. In theCentral Valley, these open country habitats have been dramatically lost oraltered, yet Swainson's hawks can and do use a variety of agricultural covertypes. Studies have found that this hawk is more abundant in areas of moderatecultivation than either grassland or areas of extensive cultivation.
The Central Valley is home to many rare and endangered species, as well asspecies now declining in California and considered for listing (candidatespecies). These special status species vary in the limiting factors thatcontribute to their rarity or decline. Three basic categories characterize thespecial status species of the Central Valley.
Category One--Species are naturally rare. Many vernal pool-adapted plants andinvertebrates are rare on a local as well as global scale because of theirlimiting habitat requirements, such as pool size and inundation period. Inaddition, these species have restricted ranges due to the limited soils andhydrologic conditions that support vernal pools. There are few species ofbirds in the Central Valley that fall into this category. Most occur in tidalmarshes, for example, California black rail and Belding's savannah sparrow.
Category Two--Species are at extralimital range. Such species are still commonwithin their continental range but have declined locally. Most of thesedeclines can be attributed to habitat loss. Western yellow-billed cuckoo andSwainson's hawks are extralimital, as they are at the western limits of theircontinental range. Habitat loss in the Central Valley has greatly impactedboth species. Although common outside of California, they are rare in thisstate.
Category Three--Species in decline globally. Species, such as peregrine falconand greater sandhill crane, are wide-ranging throughout the continent, and havedeclined throughout their range. The factors limiting peregrine falcons wasthe use of DDT, habitat loss, and falconry exploiting wild eggs. Habitat lossand human disturbance attributed to the decline of the greater sandhill cranein the Pacific Flyway.
The maintenance of bird diversity in the Central Valley will require theprotection of remaining natural communities. Agricultural lands play acritical role in this effort. As primary habitats and buffers to wildlifeareas, agricultural lands provide resources for numerous breeding species. Ifexplored, opportunities for habitat enhancement on agricultural lands can addto the natural community protection being accomplished by public agencies andwildlife conservation organizations on refuges. Private landowners can andoften develop habitat resources on their lands. Many find that the naturalcommunities can be managed to compliment their farming operations. The habitatmosaic created by private landowners will be essential in the recovery andperpetuation of California's bird life, a unique resource on the North Americancontinent.
Pied-billed Grebe - Podilymbus podiceps
Double-crested Cormorant - Phalacrocorax auritus
American Bittern - Botaurus lentiginosus
Great Blue Heron - Ardea herodias
Great Egret - Casmerodius albus
Snowy Egret - Egretta thula
Cattle Egret - Bubulcus ibis
Green Heron - Butorides virescens
Black-crowned Night-Heron - Nycticorax nyticorax
White-faced Ibis - Plegadis chihi
Canada Goose - Branta canadensis
Wood Duck - Aix sponsa
Mallard - Anas platyrhynchos
Northern Pintail - Anas acuta
Cinnamon Teal - Anas cyanoptera
Northern Shoveler - Anas clypeata
Gadwall - Anas strepera
American Wigeon - Anas americana
Common Merganser - Mergus merganser
Ruddy Duck - Oxyura jamaicensis
Turkey Vulture - Cathartes aura
White-tailed Kite - Elanus leucurus
Northern Harrier - Circus cyaneus
Cooper's Hawk - Accipiter cooperii
Red-shouldered Hawk - Buteo lineatus
Red-tailed Hawk - Buteo jamaicensis
Golden Eagle - Aquila chrysaetos
American Kestrel - Falco sparverius
Prairie Falcon - Falco mexicanus
California Quail - Callipepa californica
Virginia Rail - Rallus limicola
Sora - Porzana carolina
Common Moorhen - Gallinula chloropus
American Coot - Fulica americana
Killdeer - Charadrius vociferus
Black-necked Stilt - Himantopus mexicanus
American Avocet - Recurvirostra americana
Spotted Sandpiper - Actitis macularia
Mourning Dove - Zenaida macroura
Greater Roadrunner - Geococcyx californianus
Common Barn-Owl - Tyto alba
Western Screech-Owl - Otus kennicotti
Great Horned Owl - Bubo virginianus
Burrowing Owl - Athene cunicularia
Short-eared Owl - Asio flammeus
Belted Kingfisher - Ceryle alcyon
Acorn Woodpecker - Melanerpes formicivorus
Nuttall's Woodpecker - Picoides nuttallii
Downy Woodpecker - Picoides pubescens
Northern Flicker - Colaptes auratus
Black Phoebe - Sayrnis nigricans
Horned Lark - Eremophila alpestris
Tree Swallow - Tachycineta bicolor
Scrub Jay - Aphelocoma coerulescens
Yellow-billed Magpie - Pica nuttalli
American Crow - Corvus brachyrhynchos
Common Raven - Corvus corax
Plain Titmouse - Parus inornatus
Bushtit - Psaltriparus minimus
White-breasted Nuthatch - Sitta carolinensis
Rock Wren - Salpinctes obsoletus
Canyon Wren - Catherpes mexicanus
Bewick's Wren - Thryomanes bewickii
House Wren - Trogolodytes aedon
Marsh Wren - Cistothorus palustris
Blue-gray Gnatcatcher - Polioptila caerula
Western Bluebird - Sialia mexicana
American Robin - Turdus migratorius
Wrentit - Chamaea fasciata
Northern Mockingbird - Mimus polyglottos
California Thrasher - Toxostoma redivivum
LeConte's Thrasher - Toxostoma lecontei
Phainopepla - Phainopepla nitens
Loggerhead Shrike - Lanius ludovicianus
Hutton's Vireo - Vireo huttoni
Orange-crowned Warbler - Vermivora celata
Common Yellowthroat - Geothlypis trichas
Rufous-sided Towhee - Pipilo erythrophthalmus
California Towhee - Pipilo crissalis
Lark Sparrow - Chondestes grammacus
Sage Sparrow - Amphispiza belli
Song Sparrow - Melospiza melodia
Red-winged Blackbird - Agelaius phoeniceus
Tricolored Blackbird - Agelaius tricolor
Western Meadowlark - Sturnella neglecta
Yellow-headed Blackbird - Xanthocephalus xanthocephalus
Brewer's Blackbird - Euphagus cyanocephalus
Great-tailed Grackle - Quiscalus mexicanus
Brown-headed Cowbird - Molothrus ater
House Finch - Carpodacus mexicanus
Lesser Goldfinch - Carduelis psaltria
American Goldfinch - Carduelis tristis
Eared Grebe - Podiceps nigricollis
Clark's Grebe - Aechmorphorus clarkii
Least Bittern - Ixobrychus exilis
Redhead - Aythya americana
Swainson's Hawk - Buteo swainsonii
Caspian Tern - Sterna caspia
Forster's Tern - Sterna forsteri
Black Tern - Chlidonias niger
Yellow-billed Cuckoo - Coccyzus americanus
Lesser Nighthawk - Chordeiles acutipennis
Common Poor-will - Phalaenoptilus nuttallii
White-throated Swift - Aeronautes saxatalis
Black-chinned Hummingbird - Archilochus alexandri
Anna's Hummingbird - Calypte anna
Costa's Hummingbird - Calypte costae
Western Wood Pewee - Contopus sordidulus
Willow Flycatcher - Empidonax trailii
Pacific-slope Flycatcher - Empidonax difficilis
Ash-throated Flycatcher - Myiarchus cinerascens
Cassin's Kingbird - Tyrannus vociferans
Western Kingbird - Tyrannus verticalis
Purple Martin - Progne subis
Violet-green Swallow - Tachycineta thalassina
N. Rough-winged Swallow - Stelgidopteryx serripennis
Bank Swallow - Riparia riparia
Cliff Swallow - Hirundo pyrrhonota
Barn Swallow - Hirundo rustica
Yellow Warbler - Dendroica petechia
Yellow-breasted Chat - Icteria virens
Summer Tanager - Piranga rubra
Black-headed Grosbeak - Pheucticus melanocephalus
Blue Grosbeak - Guiraca caerulea
Lazuli Bunting - Passerina amoena
Black-chinned Sparrow - Spizella atrogularis
Black-throated Sparrow - Amphispiza bilineata
Grasshopper Sparrow - Ammodramus savannarum
Hooded Oriole - Icterus cucullatus
Northern Oriole - Icterus gabula
Lawrence's Goldfinch - Carduelis lawrencei
Barbour, M.G. and J. Major. 1977. Terrestrial vegetation of California. J.Wiley and Sons. Somerset, New Jersey.
Bellrose, F.C. 1978. Ducks, geese, and swans of North America. SecondAddition. Stackpole Books. Harrisburg, Pennsylvania.
Clark, J.L. 1992. California Wildlife Viewing Guide. Falcon Press Billings,Montana.
Cogswell, H.L. 1977. Water birds of California. University of CaliforniaPress. Berkeley, California.
Dunn, J.L. and E.A.T. Blom. 1987. Field guide to the birds of North America2nd ed. National Geographic Society. Washington D.C.
Grinnell, J. and A.H. Miller. 1944. The distribution of the birds ofCalifornia. Cooper Ornithological Club, No. 27. Washington D.C.
Harvey, T.E, K.J. Miller, R.L. Hothem, M.J. Rouzon, G.W. Page, R.A. Keck.1992. Status and trends report on the wildlife of the San Francisco Estuary.U.S.F.W.S. Sacramento, California.
Lantis, D.W. 1981. California: land of contrast. Third revision.Kendall/Hunt Pub. Co. Dubuque, Iowa.
Laudenslayer, Jr., W.F., W.E. Grenfell, Jr., D.C. Zeiner. 1991. A checklistof the amphibians, reptiles, birds, and mammals of California. California Fishand Game 77: 109-141.
McCaskie, G., P. De Benedictis, R. Erikson, J. Morlen. 1979. Birds ofNorthern California. Golden Gate Audubon Society. San Francisco, California.
Pavlik, B.M., P. C. Muick, S. Johnson, M. Popper. 1991. Oaks of California.Cachuma Press. Los Olivos, California.
Peterson. R.T. 1990. Field Guide to Western Birds. Houghton Mifflin. NewYork, New York.
Sacramento Audubon Society. 1989. Checklist of the Birds of the SacramentoArea. Sacramento Audubon Society. Sacramento, California.
Small, A. 1994. California Birds. Winchester Press.
Steinhart, P. 1990. California's wild heritage: threatened and endangeredanimals in the Golden State. California Department of Fish and Game.
Udvardy, M.D.F. 1994. Audubon Society Field Guide to North American Birds:Western Region. Alfred Knopf. New York, New York.
Prepared by: Andrew Engilis, Jr., Regional Biologist, Ducks Unlimited, Inc.Figures prepared by Paul Goebel, Engineering Technician, Ducks Unlimited,Inc.
Valley Habitats is produced by Ducks Unlimited's Western Regional Office.Items contained herein may be reproduced with permission. Copyright, DucksUnlimited, Inc., 1995.
Valley Habitats is published as part of Ducks Unlimited's VALLEY CARE Programto provide information to private land managers who wish to integrate wildlifemanagement into their existing operations.
For more information regarding conservation related land management practicescontact: Ducks Unlimited, Western Regional Office, 9823 Old Winery Place, #16,Sacramento, CA 95827
TELEPHONE: (916) 363-8257 FAX: (916) 363-9849
The National Fish and Wildlife Foundation, Hofmann Foundation and WildlifeConservation Board provided the generous funding for this issue of ValleyHabitats.