Waterfowl Energetics in the Central Valley

wetlandsby Mark Petrie, Spring 2015

The red line demonstrates available food for waterfowl from late August to early March. The blue line represents the actual food needed by birds. c/o Mark Petrie

During drought conditions in California, the red line demonstrates available food for waterfowl from late August to early March. The blue line represents the actual food needed by birds, meaning food sources will be exhausted by January. Credit: Mark Petrie

The Central Valley of California supports one of the largest concentrations of waterfowl in the world, despite losing 95% of its historic wetlands. Birds begin arriving in the Valley in late August, with most birds gone by late March. Peak numbers usually occur in December and January with the seven million waterfowl that use the valley each year relying on a mixture of wetland and agricultural habitats.

There are about 200,000 acres of wetlands in the Central Valley, of which a third are publicly managed refuges. The remainder is in private ownership and are also managed to benefit wildlife. Many of these wetlands are “summer-irrigated” in June or July to increase food production for waterfowl, much like agricultural producers irrigate crops. Rice fields that are “winter-flooded” after harvest provide the bulk of agricultural foods. About 560,000 acres of rice are planted in a normal water year, with approximately 350,000 of these acres winter-flooded. Because of the drought, 25-35% of all wetlands are expected to be dry. Few, if any, of these wetlands will be summer-irrigated because of a lack of water. Fewer wetlands and a lack of summer irrigation means that the food provided from all wetlands in the Central Valley will be half that of a normal year. Less than 400,000 acres of rice will be planted in 2015, a 30% drop from normal years. Of these 400,000 acres, we expect as little as 50,000 acres to be winter-flooded.

In normal years, the food provided by wetland and agricultural habitats is sufficient to meet waterfowl needs from late August through late March. However, the Central Valley Joint Venture (CVJV) has modeled waterfowl food supplies under 2015 drought conditions, and their results suggest that food will be exhausted by January, just as waterfowl numbers are peaking in the Central Valley (see figure below). The lack of water is also expected to increase disease outbreaks because of over-crowding, just as a lack of water for Klamath Basin refuges has increased disease there.

What can be done? Obtaining sufficient water supplies for public and private wetlands is a critical first step. This includes water supplies for summer-irrigation. Surface water supplies for winter-flooding of rice are also badly needed. Even in normal years, wetlands provide only 40% of the food required by waterfowl. We need a comprehensive drought approach that includes public wetlands, private wetlands, and agricultural habitats that are traditionally important to waterfowl in the Central Valley.