 This is because, while crows and jays die quickly from the virus, the American robin survives the virus longer, hence spreading it to more mosquitoes, which then transmit the virus to humans and other species.The American robin is active mostly during the day, and on its winter grounds it assembles in large flocks at night to roost in trees in secluded swamps or dense vegetation.The flocks break up during the day when the birds feed on fruits and berries in smaller groups.