Understanding Waterfowl: Waterfowl and the California Drought

Ducks and geese may face severe water and food shortages in the Central Valley this year

© Linda Allwein

By Mark Petrie, Ph.D.; Mark Biddlecomb; Fritz Reid, Ph.D.; and Mark Smith

This spring California's governor joined the annual trek into the Sierra Nevada mountains to measure the snowpack, which usually provides a third of the state's water. In a normal year he'd be standing on five feet of snow, but that day the only thing under his feet was grass. Although the trip was symbolic, it publicly confirmed that California was now in its fourth consecutive year of drought-the worst in recorded history. The journey down the mountain could hardly have been pleasant.

The Central Valley of California supports one of the highest densities of wintering waterfowl in the world. At times, a single refuge in the region may harbor more ducks and geese than are found in many states. These birds winter in the midst of the most sophisticated and sometimes contentious water projects in North America: the State Water Project and the Central Valley Project (CVP).

Most public and privately managed wetlands in the Central Valley obtain their water from the CVP, as do the rice and corn producers that provide crucial agricultural habitats for wintering waterfowl. The CVP is a federal water project operated by the Bureau of Reclamation. Consisting of 20 dams and reservoirs, 11 power plants, and 500 miles of major canals, the CVP stretches the full length of the Central Valley. Construction of the project began during the 1930s and was largely complete by the late 1970s. In a normal year, the CVP delivers about 2.3 trillion gallons of water for agricultural, metropolitan, and wildlife use.

The Central Valley contains two major watersheds: the Sacramento Valley in the north and the San Joaquin Valley in the south. In a drought year the CVP delivers limited water supplies based on project managers' understanding of water rights, some of which date to the mid-1800s. In general, water rights tend to be more senior in the Sacramento Valley. As a result, water shortages are often progressively worse the farther south you go in the Central Valley. Refuges and many duck clubs have long-standing, historic water rights. The CVP was amended in 1992 to provide water supplies for fish and wildlife, including water for public refuges and large blocks of private wetlands in the San Joaquin Valley's Grasslands Ecological Area, recognizing previously existing rights and mitigation for severe habitat degradation across the Central Valley. This commitment from the Bureau of Reclamation specified the delivery of a defined volume and quality of water based on biological criteria for waterfowl and wetland needs. Although these water supplies are typically reduced during a drought, cutbacks are often much greater for habitats in the San Joaquin Valley. For a variety of reasons, CVP surface-water obligations for wetlands in the San Joaquin Valley often go unmet in both drought and non-drought years.

Wintering waterfowl in the Central Valley rely on three major habitat types: managed seasonal wetlands that are flooded in the fall, rice fields that are flooded after harvest (winter-flooded rice), and harvested cornfields. To understand how the drought will impact waterfowl, we need to understand how the drought will reduce these food supplies. Under normal conditions, there are nearly 210,000 acres of managed wetlands in the Central Valley. This fall, managed wetlands will decline to somewhere between 120,000 and 150,000 acres. Few of these wetlands will be summer-irrigated, which is important for the production of waterfowl foods. Wetlands that are not summer-irrigated produce only half their normal food. Fewer wetlands, combined with a lack of summer irrigation, means that Central Valley wetlands as a whole may provide little more than a third of the waterfowl food they do in a normal year.

The loss of rice habitat may be even more dramatic. In recent years, farmers in the Sacramento Valley planted about 560,000 acres of rice. Nearly 350,000 of these acres were winter-flooded to decompose rice straw and provide crucial waterfowl food. This spring about 375,000 acres of rice were planted, and it's likely that no CVP water will be available to winter-flood any of these fields. At best, 50,000 to 75,000 acres of rice flooded with pumped groundwater may be available, depending on funding and the willingness of farmers. The drought is also impacting corn production, and waterfowl will likely see a 50 percent reduction of this food source as well.

Although agricultural habitats are less important in the San Joaquin Valley, the challenges in this region may be even more acute. The Tulare Basin, which lies at the southern end of the San Joaquin Valley, once contained a series of large lakes that provided important fall and early winter habitat, especially for northern pintails. These habitats have long since been drained, but public and privately managed wetlands in both the Tulare Basin and the Grasslands Ecological Area have essentially replaced these historical habitats. Winter site fidelity for pintails, green-winged teal, and American wigeon is high in these wetlands. These same habitats are facing some of the worst water shortages in the entire Central Valley, and additional funding to offset pumping costs or provisions for surface flooding are badly needed. Many public and private wetland managers are worried that a lack of commitment to these San Joaquin habitats will eventually produce a permanent shift in waterfowl distribution. Such a shift would undermine our attempt to maintain hunting opportunities throughout the Central Valley, and may ultimately weaken support for wetlands conservation as well.

What does this mean for the 4 million to 5 million dabbling ducks and 2 million geese that winter in the Central Valley? Dabbling ducks begin arriving in the Central Valley in late August and early September. Waterfowl numbers begin to peak in December, stay high through most of February, and then start to decline in March as ducks depart for the breeding grounds. DU and its partners have modeled the effects of fewer wetlands, little summer irrigation, and little to no winter-flooding of rice on dabbling duck food supplies. Results suggest that food resources will be exhausted by mid-winter, just as duck numbers are peaking. Although very similar conditions existed last year, food shortages were averted by a record December storm that flooded many wetlands and rice fields. While DU and its partners are working hard to find water for both wetlands and rice, a very wet winter will be needed to avoid a food shortage.

Although it's natural to focus on the drought's immediate consequences, the future implications for rice are worrisome. Winter-flooded rice fields provide nearly half of all foods for dabbling ducks in the Central Valley. These same fields produce a large amount of straw that must be eliminated prior to the next growing season. To date, winter-flooding has been an effective way to decompose straw while providing tremendous waterfowl benefits. However, this practice requires dependable and affordable surface-water supplies. Rice producers need a reliable method for decomposing straw, and many may be forced to adopt practices like baling that could reduce the food resources that rice fields provide for waterfowl. Replacing winter-flooded rice with managed wetlands that provide the same amount of food would cost $2 billion. That simply isn't in the cards, and DU is working hard to inform policymakers of what will happen if we lose this resource.

This article has focused on wintering waterfowl, but we'd be remiss if we didn't mention breeding waterfowl, especially mallards. More than half the mallards harvested in California are produced in the Central Valley and the northeastern portion of the state. This breeding population typically hovers around 400,000 birds but has steadily declined during the drought. Only 185,000 birds were surveyed in 2015, a record low. Many of these mallards rely on managed wetlands that are kept wet specifically for breeding waterfowl through the summer. The drought has made it extremely difficult to maintain many of these habitats, and the effects on waterfowl production are becoming increasingly obvious. 

Although the California drought will end, it will leave behind a legacy of challenges for those who care about waterfowl. DU and its partners will need to face these challenges with innovative solutions that address the reality of an increasingly arid west.

Dr. Mark Petrie is director of conservation planning; Mark Biddlecomb is director of operations; Dr. Fritz Reid is director of conservation programs for the Boreal and Arctic; and Mark Smith is director of public policy in DU's Western Region.