Yellow-billed Magpie. Photo: © Ashok Khosla

A study published in the Auk has revealed that the recent population crash of Yellow-billed Magpies may be due to West Nile virus. The magpie is found only in California, where populations slumped from an estimated 180,000 in 2003 to little more than half of that by 2006. The decrease correlates with the appearance of West Nile in the state in 2004. Between 2004 and 2006, more than 12,200 magpie carcasses were brought in to the California Department of Health Services. Of those that were in good enough condition to be tested, 78% were positive for West Nile.

West Nile, first recorded in the United States in 1999, has impacted bird populations (Bird Calls Vol. 11, No. 2), particularly members of the corvid family (crows, magpies, and jays), whose social behavior and carrion consumption make them particularly susceptible. Corvids are also seemingly much less able to produce antibodies necessary to fend off infection. In laboratory studies, infections in crows resulted in mortality rates of up to 100%. The magpie seems to be equally sensitive with samples taken from 21 birds eliciting only one individual with antibodies to West Nile (meaning only one in 21 birds had fought off the disease).

The Yellow-billed Magpie has a very limited range that primarily includes the Sacramento and San Joaquin valleys, but stretches as far south as Santa Barbara County. It is listed on the American Bird Conservancy/Audubon WatchList in the Yellow category, but some biologists suggest that it may warrant upgrading to Red, and potentially listing under the Endangered Species Act. Magpies are thought to help in oak seed dispersal. More study is needed to determine if their decrease has a domino effect on other aspects of the ecosystem. For more information, visit www.magpiemonitor.org.