The Value of Agriculture for Migratory Birds: Long-billed Curlews use agriculture in California???s Central Valley

Written by Melissa Pitkin/PRBO

PRBO Conservation Science, with partner Audubon California, has embarked on a study to identify important habitat types for the Long-billed Curlew Numenius americanus, a bird of conservation concern whose world population ranges from 130,000???180,000 birds. Very little is known, however, about the abundance, concentration sites, and habitat needs of this species at migratory stopovers and wintering areas, where curlews spend about nine months of the year.

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?? Stuart MacKay

To determine which habitats are important to the curlew and how many curlews concentrate in each one, PRBO is conducting two research programs: a citizen-science survey of the entire Central Valley and a satellite-tracking study of migrating curlews. Additionally, PRBO is facilitating a Masters project by Kristin Sesser of Humboldt State University who is analyzing space and habitat use of satellite tagged curlews in the Central Valley. Determining how curlews use habitats in migration and winter is critical to finding ways to protect and enhance agricultural fields and other important habitats they depend on.

Initiated in 2007, the citizen-science survey covers the Central Valley, and a tracking study, in partnership with the USGS, TNC and WWF, follows the movements of birds initially tagged on their nesting grounds in Oregon, Nevada, and Montana.

What we have learned
We are finding that important interior habitats for this species are agricultural lands, specifically alfalfa fields and irrigated pastures. Data collected by over 100 volunteers revealed that 83???94% of all birds counted during fall and winter surveys in the Central Valley in 2007 and 2008 were in alfalfa fields and pastures. Over the three surveys,15,846 (83%), 8371 (82%), and 17,117 (91%) of the curlews were from agricultural survey areas, the remainder from wildlife areas, refuges, and private wetlands.

With vast expanses of dry and irrigated pastures, alfalfa fields, and post-harvest rice fields, the interior valleys of California, combined, are likely the most important area in the world for Long-billed Curlews during migration and winter.

The telemetry research showed similar results.?? In this study, curlews were fitted with tiny satellite-transmitters while still on their nesting grounds in the grasslands of Oregon, Nevada, and Montana. Once the birds begin the migration to their wintering areas, researchers and the public can track their progress via the internet.

The Oregon birds all travelled to the Central Valley and the Nevada birds to California and Mexico. Those stopping in California use alfalfa fields, pastures, and other agricultural lands for their wintering habitats.?? Most curlews banded in Montana?? travelled to wintering sites in Texas and Mexico.

Both these research projects underscore the importance of irrigated agriculture for wildlife. In addition to the curlews, hundreds of thousands of shorebirds rely on irrigated pastures and rice fields as surrogate wetlands.?? California???s Central Valley has changed dramatically over the last 100 years as natural seasonal wetlands have been converted to agriculture and development. Now agricultural fields, along with managed wetlands, can provide those critical habitats in California???s Central Valley. This ongoing research project seeks to further document shorebird use of natural and managed wetlands, along with agricultural crops, with the aim of protecting and enhancing wetland habitat in California.

Shuford, W. D.*, G. M. Langham???, G. W. Page*, and C. Hickey*. 2009. Distribution, abundance, and habitat use of Long-billed Curlews in California???s Central Valley from broad-scale surveys in 2007 and 2008. Central Valley Bird Club Bulletin 12:29???44.

*PRBO Conservation Science, 3820 Cypress Drive #11, Petaluma, CA 94954
???Audubon California, 765 University Avenue, Sacramento, CA 95825

Interesting Facts About Long-billed Curlews:

  • Both males and females incubate eggs in nests that they scrape out of the ground using their feet and chests.
  • Curlews??? mottled brown and black plumage makes them very difficult to see in the heavily grazed grasslands where they like to nest.
  • Curlews defend their nests and young by feigning injury to lure predators away.
  • The bills of female curlews are longer, flatter and more curved than those of the males, making it possible for?? knowledgeable people to tell males from females in the field.
  • Curlews eat a wide variety of prey, including beetles, grasshoppers, earthworms, crayfish, marine crabs, and ghost shrimp.

More info: Melissa Pitkin, Education and Outreach Director, (707) 781-2555 ext 307 (Tue-Thurs), (415) 868-0655 ext 305 (Mon & Fri), 3820 Cypress Drive #11, Petaluma, CA 94954

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