Declines of Black-Billed Magpie (Pica hudsonia) and Black-Capped Chickadee (Poecile atricapillus) in the North-Central United States Following the Invasion of West Nile Virus

• Published in: Western North American naturalist Vol. 80; no. 2; pp. 204 - 214
• Main Authors: Brenner, Stephen J., Jorgensen, Joel G.
• Format: Journal Article
• Language: English
• Published: Provo Brigham Young University 01.07.2020; Western North American Naturalist
• Subjects: Abundance; Animal behavior; Birds; Clines; Mortality; Mosquitoes; Pica hudsonia; Poecile atricapillus; Precipitation; Regions; Species; Studies; Viruses; West Nile virus; Iowa; Great Plains; United States > US; North America
• ISSN: 1527-0904; 1944-8341
• DOI: 10.3398/064.080.0208

West Nile virus (WNV) is an introduced pathogen, transmitted by mosquitos, that spread across North America following its arrival there in 1999. Birds host the virus, but consequences of the disease to bird species have been variable. A small number of avian species are especially susceptible to WNV, experience high mortality rates when infected, and have shown regional declines apparently because of the disease. Other species have seemingly been unaffected. Transmission of WNV is associated with climate, with higher incidence of transmission in dry areas with warm winters. The north-central United States is an area that exhibits clines in temperature and precipitation, and in this area changes in species abundance due to WNV have not been closely examined. We used Christmas Bird Count (CBC) data to investigate changes in winter abundance of selected species before and after the arrival of WNV in the Great Plains. After arrival of WNV, average estimated abundances of Black-billed Magpie (Pica hudsonia) were significantly lower than projected abundances across much of the Great Plains. Black-capped Chickadee (Poecile atricapillus) abundances reached their lowest counts in portions of the Great Plains immediately after the arrival of WNV and experienced overall negative annual declines from 1988 to 2017. Two other species that were examined did not experience changes in abundance across the study area. Abundances of Black-billed Magpies and Black-capped Chickadees have declined over the past 30 years in the Great Plains, and WNV has likely played a major role in recent declines of magpies throughout the study area.