The Land Where Birds Are Grown

A visit to the engineered wetlands of California’s intensively cultivated Central Valley.

Arctic-nesting geese at the Merced National Wildlife Refuge
Merced National Wildlife Refuge, California. [Cynthia Hooper]

Remaking California’s Central Valley wetlands was a complicated project that took much of the 20th century. Resurrected from degraded farmland and cash-strapped gun clubs, assembled by bulldozer and backhoe, the current patchwork of national wildlife refuges, state wildlife areas, and county preserves is much diminished from the four million acres of primeval wetlands that spanned the Central Valley before it was farmed. Nevertheless, these habitats are ecologically significant on a hemispheric level, serving 60 percent of migratory waterfowl on the Pacific Flyway, including three million ducks, two million geese, and a half million shorebirds. Their restoration has lured hungry birds away from agricultural fields, created wilderness access for rural communities, and returned endangered species to viable numbers. Decades before the spread of concepts like the Anthropocene and reconciliation ecology, refuge managers were devising ways to sustain ecological systems that had been dramatically altered. 1

Decades before the spread of concepts like the Anthropocene, refuge managers were devising ways to sustain ecological systems that had been dramatically altered.

Today there are about 206,000 acres of actively managed wetlands in the Central Valley, a third of which are publicly owned. Some, like the Sacramento and San Luis National Wildlife Refuges, are popular with urban tourists, featuring visitor centers, well-maintained auto tours, and interpretive signage; others, like the state-run Mendota and Volta Wildlife Areas, are managed for hunting rather than wildlife observation. Roadside wilderness zones, irrigation canals, and levees along the refuge boundaries provide opportunities for unsanctioned recreation and foraging. 2

Maintaining functional wetlands in a 21st-century landscape dominated by agriculture and cities requires a host of hard and soft infrastructures. Canals, pumps, and sluice gates provide critical life support, and the lands are irrigated and tilled in seasonal cycles to essentially farm wildlife. 3 Reams of laws and regulations scaffold the system. The federal Central Valley Project Improvement Act (1992) — perhaps the most critical of these laws — establishes a minimum water supply for nineteen valley refuges, though this water can be unaffordable, undeliverable, and politically contested. 4

The videos published here record seasonal shifts at thirteen managed wetlands in the valley’s major drain basins — the verdurous Sacramento River Valley, the extensively re-engineered San Joaquin River floodplain, and the agro-industrial Tulare Basin. My ongoing documentary project Cultivated Ecologies observes interactions between humans, wildlife, and infrastructure in these novel ecosystems.

The Tulare Basin

Satellite views of the Tulare Basin, California
Left: Development in the Tulare Lakebed. Right: Kern National Wildlife Refuge (lower center), with evaporation basins managed by the Tulare Lake Drainage District to the north. [USDA]

Cynthia Hooper, Cultivated Ecologies: The Tulare Basin, 2018.

California’s largest expanse of primeval wetlands was found in the Tulare Basin. Once enormous Tulare Lake anchored these wetlands and episodically flooded northward to the San Joaquin River on its way to the ocean. Tulare Lake was drained by the turn of the 20th century, but sections of its now-leveed footprint can still rise from the dead during periods of exceptional rainfall. Industrial agriculture completely dominates this basin, enabled by the California Aqueduct along the west side, the Friant-Kern Canal on the east, and copious groundwater pumping. The Tulare Basin now has no natural outlet and more than 99 percent of its wetlands are gone.

The Kern National Wildlife Refuge features seasonal wetlands that are flooded each winter with CVPIA water, as well as grassland, scrubland, and alkali playa that rely mostly on scarce rainfall. Plenty of birds find a home here, including up to 6,000 nesting White-faced Ibis that commandeer the place each spring. 5 Like much of the Tulare Basin, parts of this refuge suffer from surface and groundwater contamination by salt from extensive irrigation. Kern also sits uncomfortably close to more than 3,000 acres of toxic evaporation ponds that many birds find appealing — particularly migratory shorebirds like Black-necked Stilts and American Avocets. Tactics for keeping the birds away include maintaining a 300-acre compensation habitat for alternative nesting and foraging. This extremely subtle wilderness, near the original north shore of Tulare Lake, almost invisibly blends into the row crops that surround it. 6

The Tulare Basin’s other significant wetlands include the Mendota Wildlife Area, a state refuge managed for hunting and for growing irrigated crops of safflower and watergrass to feed its huge population of birds; and the isolated Pixley National Wildlife Refuge, surrounded by dairies and field crops and dependent on a single source of management water from a CVPIA-funded well. Pixley’s seasonal wetlands, moist soil units, and upland habitat support a dedicated flock of up to 7,000 Sandhill cranes.

The San Joaquin Basin

Satellite views of the San Joaquin Basin and the Volta Wildlife Area
Left: Lower San Joaquin Basin, with San Luis National Wildlife Refuge (upper left), Grasslands Wildlife Management Area (center bottom), and the city of Merced (upper right). Right: Volta Wildlife Area. [USDA]

Cynthia Hooper, Cultivated Ecologies: The San Joaquin Basin, 2017.

Upstream from the Sacramento-San Joaquin Delta, the once-mighty San Joaquin River nurtured an enormous floodplain with great expanses of wetlands, grasslands, vernal pools, and alkali sinks. The construction of the Central Valley Project (1933) and later the California State Water Project (1960) completely transformed the hydrology of this watershed, yet it still supports the largest contiguous wetlands in all California, with numerous public and private refuges. The greatest of these is the privately owned Grasslands Wildlife Management Area, a sprawling mosaic of duck hunting clubs and cattle ranches that collectively manage their land for waterfowl habitat with perpetual conservation easements, a public water district, and a permanent contract for CVP water.

Nearby, the state-run Volta Wildlife Area features intensively managed seasonal wetlands and an enormous irrigation canal that dramatically slices the refuge in half. Flanking this canal, two cascading groundwater production wells disgorge CVPIA water for Volta and additional refuges downstream. High-tech sensing equipment monitors salt, selenium, boron, arsenic, and nitrate levels in the canal, and determines how much clean surface water must be mixed with produced groundwater to make the recipe acceptably safe for wildlife. 7 Among the many species served, the Volta refuge hosts the region’s earliest migrating Northern Pintail ducks, and provides critical habitat for the giant garter snake — a threatened species found only in the Central Valley.

The San Joaquin Basin’s other significant wetlands include the diverse habitats of San Luis National Wildlife Refuge and Merced National Wildlife Refuge. Merced’s expansive ponds are covered every winter in cacophonous blankets of 60,000 arctic-nesting geese, and more than 20,000 Lesser Sandhill cranes (the largest population on the Pacific Flyway) arrive each season to feast in cornfields grown especially for them. This corn also feeds the geese and many small mammals, which in turn are consumed by numerous raptors. Merced is a completely spectacular place — one of the best valley refuges in winter for its sheer concentration of birds.

The Sutter and Yolo Basins

Satellite views of the Sutter National Wildlife Refuge and the Fremont Weir Wildlife Area, Sacramento Valley Flood Control Project.
Left: Sutter Bypass and Sutter National Wildlife Refuge. Right: Fremont Weir Wildlife Area. [USDA]

Cynthia Hooper, Cultivated Ecologies: The Sutter/Yolo Basins, 2018.

Further north, the Sacramento River and its tributaries once regularly exploded into a vast inland sea that could reach 100 miles long and up to 8 miles wide. These historical flood regimes naturally irrigated the Sacramento Valley’s many freshwater marshes, floodplains, and dense riparian forests, until gold miners and farmers arrived and began a relentless series of battles to control the epic deluges, culminating in the Sacramento Valley Flood Control Project. This gravity-fed system comprises more than 1,000 miles of huge earthen levees, six weirs (low dams), and two major bypass structures that roughly follow the historic floodplains, intercepting the Sacramento River’s overflow at critical junctures. When the project was near completion in the mid-1930s, almost all remaining wetlands in the valley had been drained and plowed under, primarily for rice cultivation, which still dominates today. 8

The northernmost major bypass hosts the Sutter National Wildlife Refuge, which also functions as one of the Sacramento Valley’s re-engineered floodplains. In some years it is under up to ten feet of water. As many as 73,000 ducks and 100,000 geese use the refuge each winter, as do migrating salmon during periods of high flow. At the base of the Sutter Bypass, the state-run Fremont Weir Wildlife Area has a two-mile-long, six-foot-high vintage concrete weir that calms the velocity of floodwaters entering the Yolo Bypass on their way to the Sacramento-San Joaquin Delta. This weir has long been an obstacle for migrating fish, but a newly-installed notch helps waylaid fish find their way back to the Sacramento River’s main channel. Further downstream, the state’s Yolo Bypass Wildlife Area includes bountiful agricultural fields and cattle-grazed grasslands alongside seasonal and permanent wetlands. Rice, corn, safflower, and sunflower crops feed local and migratory birds and are also sold to fund refuge operations. 9

The Colusa and Butte Basins

Satellite views of the Sacramento National Wildlife Refuge and the Colusa and Butte Basins.
Left: Colusa and Butte Basins, on either side of the Sacramento River. Right: Sacramento National Wildlife Refuge, surrounded by rice fields. [USDA]

Cynthia Hooper, Cultivated Ecologies: The Colusa/Butte Basins, 2017.

The Colusa and Butte basins flank each side of the Sacramento River’s alluvial levees as it meanders just west of the Sutter Buttes — a tiny volcanic mountain range majestically sited in the center of the Sacramento Valley. Together these basins have six major refuges, including three shown in this video: Colusa National Wildlife Refuge, Gray Lodge Wildlife Area, and Sacramento National Wildlife Refuge. The popular and accessible Sacramento refuge occupies former farmland where no significant wetlands existed historically. It was devised in 1937 as a complex of irrigated rice fields and ponds to feed migrating waterfowl and give them some cover from the crosshairs of hunters. The refuge now supports as many as 750,000 ducks, 200,000 geese, and 80,000 annual human visitors. 10

Sacramento’s seasonal wetlands are managed like many others in the Central Valley, starting with a late summer flood-up to a water depth of no more than twelve inches, for optimal foraging by early-arriving dabbling ducks and geese. Ponds are kept flooded through the winter so the birds can feed, loaf, and court, and so that human visitors can either observe them or shoot them. Flooded units are then gradually drawn down in the spring, as waterfowl head north and migrating shorebirds arrive to probe the moist soil for nutritious invertebrates. After draining, the wetlands are irrigated at least once in the summer to germinate beneficial food plants like smartweed, swamp timothy, and millet. As these food plants mature, the fall flood-up begins, migrating waterfowl return, and the cycle starts anew.

The more than half million acres of privately owned Sacramento Valley rice operations are a critical food source as well. Since the 1990s, costly crop depredations have been curtailed by the adoption of early-maturing rice strains that are harvested before most migrating birds return in the fall. Once the harvest is complete, the fields are typically flooded to allow birds to forage for waste grain, weed seeds, and invertebrates left in the mud. Post-harvest rice fields contain only about half the nutritional value (per acre) of managed wetlands, but they provide most of the food for the Central Valley’s wintering waterfowl. 11

Wetland Futures

Fish passage structure, Fremont Weir Wildlife Area
Fish passage structure, Fremont Weir Wildlife Area. [Cynthia Hooper]

The engineered wetlands of California’s Central Valley are powerful places for considering our ecological past and future. They arose from an ethos of technocratic land management that assumed mastery and control over natural resources, and they still honor the Progressive-era assertion that public access to wilderness promotes social harmony and clarifies the common good. 12 Though these refuges focus more on the maintenance of targeted species than on the preservation of magnificent scenery, they nevertheless provide visitors with accessible and meaningful aesthetic experiences. At this divisive moment in our national narrative, they are especially valuable as ideologically inclusive public lands that are valued by rural and working-class communities.

Yet these sites are also entangled within global commodity systems and outmoded infrastructures. As water becomes more costly and scarce, and more challenging to manage and store, crops with a higher return per irrigated acre — like nut orchards and vineyards — will continue to replace habitat-valuable crops like rice and alfalfa. The changing climate also alters the carrying capacity of wetlands and shifts the migration and foraging patterns of birds and other wildlife. As Central Valley cities expand, the ongoing conversion of farmland to hardscape will further shrink habitat. 13

Wetlands are naturally dynamic systems that can withstand episodic degradation, so long as the links in migration corridors are actively maintained. 14 Studying legacy ecological practices in California’s Central Valley gives us insight about how to prepare for future climate change. As threats accelerate, preserving wetlands will require new technologies and adaptive management strategies, as well as more active collaborations between farmers, wildlife managers, and citizen scientists. 15 These hybrid landscapes are compelling models for how to synchronize biological and infrastructural systems. As we soberly face a new climate paradigm, they deserve our vigorous defense.

Colusa National Wildlife Refuge
Colusa National Wildlife Refuge. [Cynthia Hooper]

  1. See Philip Garone, The Fall and Rise of the Wetlands of California’s Great Central Valley (University of California Press, 2011). This project was inspired by this exhaustively researched book and owes an enormous debt of gratitude to it. For bird population counts, see Garone, 8; and Central Valley Joint Venture, Central Valley Joint Venture Implementation Plan – Conserving Bird Habitat, (U.S. Fish and Wildlife Service, 2006), 2 [PDF]. By comparison, in the 19th century the Central Valley was used by an estimated 20 to 40 million migratory waterfowl.
  2. Central Valley Joint Venture, 28. For a detailed description of the variety of sanctioned and unsanctioned uses for rewilded California landscapes, see Brett Milligan and Alejo Kraus-Polk, Human Use of Restored and Naturalized Delta Landscapes (UC Davis Center for Watershed Sciences, 2016), 45-63 [PDF].
  3. See Brett Milligan, “Landscape Migration,” Places Journal, June 2015, Milligan describes the process of farming wildlife in the “walking wetlands” of the Klamath Basin, on the Oregon-California border, as well as the role of biophysical landscapes as infrastructure for systems of production.
  4. Meghan Hertel, “No, the Central Valley Refuges Aren’t Getting 100% of Their Federal Water Allocations,” Audubon Blog, April 2016. See also Central Valley Joint Venture, 12.
  5. Kern and Pixley National Wildlife Refuges: Final Comprehensive Conservation Plan (U.S. Fish and Wildlife Service, 2005), 27-28 [PDF]. The CVPIA Refuge Water Supply Program has been instrumental in returning bird species like the White-faced Ibis and Sandhill Crane to abundant numbers in the Sacramento Valley and the Tulare Basin. See Central Valley Joint Venture, 229-30.
  6. The California State Water Project and the federal Central Valley Project annually import over one million tons of salt into the Tulare Basin. Other sources of salt include municipal wastewater disposal, oil field brines, confined animal facilities, fertilizer application, evapoconcentration, and naturally occurring salt. See Gail Cismowski, et al, Salinity in the Central Valley: An Overview (Central Valley Regional Water Quality Control Board / California Environmental Protection Agency, 2006), 1-35 [PDF]. From 1974 to 1979, the Tulare Lake Drainage District built the North, South, and Hacienda Evaporation basins immediately north of the Kern refuge to permanently store subsurface agricultural return flows. After the discovery of lethal levels of selenium concentrations at the Kesterson National Wildlife Refuge in 1983, these and other Tulare Basin evaporation sumps were similarly determined to have the concentrated levels of selenium that cause reproductive harm to birds. See Garone, 231-36, and Mark Arax and Rick Wartzman, The King of California: J.G. Boswell and the Making of A Secret American Empire (PublicAffairs, 2003), 388-402. Despite the modest effort of creating compensation habitat, the Tulare Basin’s drainage crisis is acute and steadily worsening, as agriculture companies work hundreds of thousands of profitable acres until they are useless for anything except solar farms. See John Letey, “Soil Salinity Poses Challenges for Sustainable Agriculture and Wildlife,” California Agriculture, Vol. 54, No. 2 (March 1, 2000), 43-48,
  7. Biological Assessment for the Volta Wildlife Area Level 2 Diversification/Incremental Level 4 Development Pilot Project, Appendix B: Project Monitoring Plan (U.S. Bureau of Reclamation, 2010).
  8. For a history of these flood control efforts, see Robert Kelley, Battling the Inland Sea, (University of California Press, 1989). For a helpful overview of current infrastructure, see Jay R. Lund, “Sacramento River Flood Control Project,” UC Davis Center for Watershed Sciences.
  9. Sacramento, Delavan, Colusa, and Sutter National Wildlife Refuges Final Comprehensive Conservation Plan and Environmental Assessment (U.S. Fish and Wildlife Service, 2009), 41 and 91 [PDF]. The automated gate in the Fremont Weir’s new fish passage structure is designed to help control the timing, duration, and frequency of flooding downstream. Recreating the slower and shallower water of the Yolo Basin’s ancestral floodplain facilitates the growth of phytoplankton, which feeds more zooplankton, which in turn feeds more juvenile salmonids. See Jeffrey J. Opperman, et al., Floodplains: Processes and Management for Ecosystem Services (University of California Press, 2017), 182-198.
  10. Garone, 152-155; Robert M. Wilson, Seeking Refuge: Birds and Landscapes of the Pacific Flyway (University of Washington Press, 2010), 82-90; and Sacramento, Delevan, Colusa, and Sutter National Wildlife Refuges Final Comprehensive Conservation Plan, 11 and 118.
  11. Central Valley Joint Venture, 46-50
  12. See Jedediah Purdy, After Nature: A Politics for the Anthropocene (Harvard University Press, 2015), 162-80.
  13. Central Valley Joint Venture, 203; and Brian Van Lienden, et al., Sacramento and San Joaquin Basins Climate Impact Assessment (U.S. Bureau of Reclamation, Mid-Pacific Region, 2014), 2 [PDF]. Urban encroachment in the Central Valley is projected to take 1.7 million irrigated acres out of production by the end of the century. That represents 23 percent of the current acreage.
  14. Wilson, 16-18.
  15. See Anne Canright, “Pop-Up Wetlands: A Success Story,” Breakthroughs (UC Berkeley College of Natural Resources), Fall 2014.
Cynthia Hooper, “The Land Where Birds Are Grown,” Places Journal, January 2019. Accessed 31 May 2023.

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