In this Aug. 31, 2017 photo, Dr. <PERSON>, director of animal health at the Dallas Zoo in Dallas injects a solid birth control implant to a helmeted guineafowl as <PERSON>, vet tech, assists. The Dallas Morning News reports experts say zoos use birth control as part of breeding recommendations, space constraints and health concerns -- all done under the careful watch of keepers. ( <PERSON>/The Dallas Morning News via AP)