The 16-foot tower is the fourth being built in the area as part of a conservation project through the National Audubon Society. The bird, whose natural habitat is hollow logs in forests, has adapted to building its nests and roosting in chimneys. But even chimneys are in short supply these days. The population has dropped by 50 percent since records have been kept, said Mississippi River Field Institute Director Reed Bishop. The towers will provide a safe place for the migratory birds to nest and roost. The $500 in materials needed to build each tower was donated by Mississippi Section of the American Chemical Society. Anyone interested in building a tower can contact the Audubon Society for instructions.