The whooping crane is one of the rarest birds in North America. It is also the tallest with adults approaching five feet in height. Males are slightly larger than females. Whooping cranes mate for life and can live nearly 30 years in the wild, and 35 to 40 years in captivity. All of the whooping cranes alive today; both wild and captive; are descendents of the last 15 remaining cranes that were found wintering in Texas in 1941. They were named an endangered species in 1967 and due to conservation efforts, the number of whoopers has increased. As of April 2007 there were about 340 whooping cranes living in the wild, and another 145 living in captivity. The only natural wild flock of Whooping Cranes nests in Wood Buffalo National Park in the Northwest Territories of Canada. Each fall, the whoopers fly 2500 miles from Wood Buffalo National Park to their wintering grounds at Aransas National Wildlife Refuge.