, Volume 4, Issue 1, pp 18-24

First online:

West Nile Virus and California Breeding Bird Declines

  • Walter D. KoenigAffiliated withHastings Reservation, University of California Berkeley Email author 
  • , Lauren MarcusAffiliated withCalifornia Department of Health Services
  • , Thomas W. ScottAffiliated withCenter for Conservation Biology, University of California
  • , Janis L. DickinsonAffiliated withLaboratory of Ornithology, Cornell University

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Since it was first detected in 1999, West Nile virus (WNV) quickly spread, becoming the dominant vector-borne disease in North America. Sometimes fatal to humans, WNV is even more widespread among birds, with hundreds of species known to be susceptible to WNV infection in North America alone. However, despite considerable mortality and local declines observed in American crows (Corvus brachyrhynchos), there has been little evidence of a large regional association between WNV susceptibility and population declines of any species. Here we demonstrate a correlation between susceptibility to WNV measured by large-scale testing of dead birds and two indices of overall population change among bird species following the spread of WNV throughout California. This result was due primarily to declines in four species of Corvidae, including all species in this family except common ravens (Corvus corax). Our results support the hypothesis that susceptibility to WNV may have negative population consequences to most corvids on regional levels. They also provide confirmation that dead animal surveillance programs can provide important data indicating populations most likely to suffer detrimental impacts due to WNV.


avian populations Breeding Bird Survey Corvidae vector-borne disease