Field-based estimates of avian mortality from West Nile Virus infection

Michael P. Ward, Tara A. Beveroth, Richard Lampman, Arlo Raim, David Enstrom, Robert Novak

Research output: Contribution to journalArticlepeer-review


One of the unique characteristics of West Nile virus (WNV) in North America is the large number of bird species for which the virus can be fatal. WNV mortality has been documented through experimental infections of captive birds and necropsies of free-ranging birds. Investigations of WNV-related mortality in wild birds often focus on species with dramatic population declines (e.g., American Crow, Corvus brachyrhynchos); however, few studies have addressed WNV-related mortality in species not exhibiting marked population declines since the arrival of WNV. We conducted a mark-recapture study of 204 Northern Cardinals (Cardinalis cardinalis) in an area with endemic WNV activity to estimate WNV-related mortality. Previous research has shown that once a bird is infected and recovers from WNV it develops antibodies making it resistant to future infection. Assuming that mortality risks from non-WNV causes were the same for individuals with (had been exposed to WNV) and without antibodies (had not been exposed to WNV), we compared the survival rates of birds with and without WNV antibodies to estimate the impact of WNV on wild birds. An information theoretic approach was used, and the apparent survival was found to be 34.6% lower for individuals without antibodies during the period when WNV was most active (July-September). However, the apparent survival rate was 9.0% higher for individuals without antibodies over the rest of the year. These differences in apparent survival suggest that WNV increases mortality during the WNV season and that chronic effects of WNV infection may also be contributing to mortality. Although WNV appears to have increased mortality rates within the population, population trend data do not indicate declines, suggesting that some cardinal populations can compensate for WNV-related mortality.

Original languageEnglish (US)
Pages (from-to)909-913
Number of pages5
JournalVector-Borne and Zoonotic Diseases
Issue number9
StatePublished - Nov 1 2010


  • Apparent survival
  • Exposure rate
  • Northern Cardinal
  • Serology
  • West Nile virus

ASJC Scopus subject areas

  • Microbiology
  • Infectious Diseases
  • Virology


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