 Birds in central California of the western subspecies "propinquus" are considered to be still increasing their range, and this is probably the case elsewhere in the U.S.The American robin is a known reservoir (carrier) for West Nile virus.While crows and jays are often the first noticed deaths in an area with West Nile virus, the American robin is suspected to be a key host, and holds a larger responsibility for the transmission of the virus to humans.