Urban Ills
Crows in cities hit harder by West Nile virus
American crow populations declined more severely in urban than rural areas after West Nile virus reached the northeastern US, according to a study in Ecological Research.
West Nile virus made its first reported appearance in the US in 1999. The virus is carried by mosquitoes and can infect birds and humans. American crows (Corvus brachyrhynchos) are particularly vulnerable and usually die after infection, the authors say.
The team examined records from the North American Breeding Bird Survey, a citizen science effort to count birds along specific routes. In the northeastern US, the abundance of American crows quickly dropped from 1999 to 2004. But not all populations were equally affected. Crows that lived in more forested, rural areas didn’t decline as much as crows in urban areas, the authors found.
Crow abundance dropped more in the years following warm winters, and urban areas tended to be warmer than rural areas. So the team isn’t sure whether urban crows are more susceptible to West Nile virus because of higher temperatures – which could boost mosquito survival and virus transmission – or because the cities’ sewer and water systems encourage mosquito breeding. – Roberta Kwok
Source: LaDeau, S.L., Calder, C.A., Doran, P.J., & P.P. Marra. 2010. West Nile virus impacts in American crow populations are associated with human land use and climate. Ecological Research DOI: 10.1007/s11284-010-0725-z.
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