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Flocking to Flooded Fields in the Central Valley

A Shorebird Saga

Khara M. Strum


Tucked into the soft grasses and mosses of a tundra wetland, Long-billed Dowitcher chicks emerge in mid-summer from their brown-splotched eggs. From now on, their lives will be linked to places where water saturates land. Only four weeks later, when similar to adults in size but still wearing the drab grey plumage of juveniles, they'll be on their own, testing their wings and gaining strength. Guided by instinct, the young will soon follow their elders to the prey-rich marshes and estuaries along the northwestern Alaskan coast.

At these migration staging areas, dowitchers forage in mixed flocks with other species of shorebirds to exploit abundant food resources and accumulate fat reserves that will carry them on the first leg of their journey south. They also depend upon such habitats during migration, to replenish their energy reserves--even though much of North America's freshwater wetlands have been lost.
A Long-billed Dowitcher in favored feeding habitat. Photo by Tom Grey.

Wetlands provide the soft, muddy substrates preferred by so many shorebird species: they probe the dark and muddy bottoms with their sensitive bills for buried treasures--small aquatic invertebrates. Due to the rare and ephemeral nature of wetland habitats, shorebird flocks often number in the tens of thousands at important stop-over areas. Many such sites (including some in California, thanks to the work of PRBO) are designated by the Western Hemisphere Shorebird Reserve Network (www.whsrn.org) for their value to migratory shorebird populations.

California's Central Valley, even after 100 years of altered landscapes and regulated water management, remains a major avenue in the Pacific Flyway: countless shorebirds migrate and spend the winter here. As detailed throughout this Observer, the region's water regime is subject to historical and ongoing radical change, with a warming climate posing unprecedented stresses. Whether and how the Long-billed Dowitcher and other shorebirds will succeed in meeting their habitat needs are questions of central importance to PRBO.
Especially during migration, shorebirds such as the Long-billed Dowitcher rely on Central Valley habitats. Photo by Peter Latourrette / www.birdphotography.com.

The first adult Long-billed Dowitchers arrive in the northern Central Valley in July from their Arctic breeding grounds, and their search for habitat is intense. The shallow, open-water habitat they need is scarce at that time, as most flooded habitat then is locked into densely growing rice or relatively deep permanent wetlands. Early in the fall, Long-billed Dowitchers and other shorebirds find refuge in waste-water treatment and evaporation ponds.

As fall advances, farmers harvest crops and prepare fields for the winter, and water is delivered to break down the crop remains without burning. These flooded lands--thousands of acres of potential habitat for shorebirds--represent a major proportion of the wet habitat across the landscape in winter. The Long-billed Dowitcher, with its rapid up-and-down "sewing-machine" motion, will forage in water up to its belly, often submerging its head and bill entirely, but is limited to shallow-water habitats, which it seeks across rice fields and managed wetlands alike.

Recognizing the huge habitat resource represented by winter-flooded rice in the Sacramento Valley, PRBO Conservation Science, in partnership with Audubon California, The Nature Conservancy and other Central Valley Joint Venture partners, has joined forces with the California Rice Commission to develop ways of further enhancing wet agricultural land for wintering shorebirds and other waterbirds. Flooded rice provides over 60% of the waterbird habitat available in the Central Valley in winter. We are evaluating ways of creating shallow-water shorebird habitat at little or no cost to the rice growers and without radically changing their current flooding practices.

As important as post-harvest flooded crop fields are, their future is uncertain. Climate change looms as an overwhelming influence and may cause a shift in what kinds of crops growers can produce in the Central Valley. Warmer weather will likely favor hot-season crops (such as melon and sweet potato) over warm-season ones (rice and corn). With changing agricultural practices in the valley and predicted reductions in the Sierra snowpack could come reductions in the acreage that is winter-flooded--and in shorebird and other waterbird habitat.

Issues related to water and wetland habitats are complex. Apart from a warming regime--sure to intensify the challenges--water is a tightly managed commodity today, and any potential re-allocation has consequences for wildlife.