Crows are associated with death, but not like this. Numbers of crows and the related blue jay in the north-eastern US are down by nearly half in some places. The cause is West Nile virus, responsible for 179 human deaths since it arrived in North America in 1999, and which is carried mainly by birds.
鈥淲e knew the mosquitoes that carry the virus feed heavily on certain birds, yet we weren鈥檛 finding survivors with antibodies,鈥� says Marm Kilpatrick of the Consortium for Conservation Medicine in New York. 鈥淭hat suggested they were dying.鈥� Sure enough, surveys have showed abrupt declines after 1999 in titmice, wrens, chickadees and American robins 鈥� but also, unexpectedly, bluebirds.
This may mean that other species not in the surveys are also suffering. Birds of prey are a particular worry, Kilpatrick says.
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Journal reference: Nature (DOI: 10.1038/nature05829)
