Eagle Mountain is a multi-faceted eagle preservation, education, and entertainment complex with an aviary featuring the largest exhibition of non-releasable American bald eagles in America in their natural habitat. These birds are deemed non-releasable by the U.S. Fish and Wildlife Service because they would not be able to survive in the wild. The project is a cooperative effort between Dollywood and the American Eagle Foundation, a non-profit organization permitted by the U.S. Fish and Wildlife Service and the Tennessee Wildlife Resources Agency to possess, care for, exhibit, rehabilitate, and breed birds of prey. The bald eagle has been the national symbol since 1792, though Benjamin Franklin preferred the wild turkey. Its name comes from the Olde English word balde, meaning white, as in white-headed eagle. Bald eagles' heads and tails change from dark brown to white when they reach sexual maturity, usually between 4 and 5 years of age. They have been recorded living up to 39 years in the wild and over 50 years in captivity, and their flight speed during flapping and gliding has been measured between 36 and 44 miles per hour. More than 12,000 pairs were nesting in the lower 48 states in 2009. Bald eagles begin arriving in Tennessee in late October and peak in late January to mid-February, with the state's winter population peaking at 300 to 400 eagles, most at Reelfoot and Dale Hollow Lakes. Nesting declined in the 1950s mainly because of D.D.T., which made eggs infertile or shells too thin, but since the ban of D.D.T. in 1972, the eagle population has steadily grown, and most of the wintering eagles come from Canada and the Great Lakes.