Whooping cranes are North America's tallest bird, but their numbers are being cut short at a dramatic pace, according to the U.S. Fish and Wildlife Service. The species — which nearly went extinct in the 1940s but has since bounced back to 539 birds — died at about twice the normal rate last year and will suffer an overall population drop, raising concerns about whether it can continue its comeback. Scientists aren't sure what exactly caused the sudden decline, but habitat loss and diseases like West Nile Virus are some of the biggest threats facing whooping cranes. (Source: AP)
