Scientists attempt to breed new generations of nearly extinct species. The loneliest animals are the most endangered species on the planet. Collected and protected by dedicated scientists, these animals represent the end of the line for their species. In many cases, intensive captive breeding programs have been launched with the aim of sustaining these animals and the hope of returning them to the wild. Viewers are taken into high-security, high-tech labs where scientists attempt to breed new generations and into the field to discover what forces have led to the demise of entire species. Featured animals include Yangtze turtles under 24-hour surveillance; a baby Sumatran rhino; a special collection of lemurs; the Spix's macaw, a bird declared extinct in the wild in 2000; and "Lonesome George," a giant tortoise from the Galapagos, who is the last of his kind. NATURE: The Loneliest Animals airs Wednesday, March 20, 2013 at 8 p.m. on WXXI-TV/HD (DT21.1/cable 11 and 1011).