Frozen semen helps save endangered species U.S. National Zoo scientists have used frozen semen to help save the black-footed ferret, one of the most endangered species on Earth. Two black-footed ferrets at the zoo have each given birth to a kit that was sired by males that died in 1999 and 2000. Officials said the two ferrets were artificially inseminated in May with frozen semen from the two deceased males whose sperm samples were collected and frozen in 1997 and 1998. Once believed extinct, 18 black-footed ferrets discovered in 1981 were removed from the wild to establish a captive breeding and recovery program in Wyoming. The National Zoo's Conservation and Research Center in Front Royal, Va., said it was the first institution outside of Wyoming to breed the species. National Zoo scientists said they also developed the first successful artificial insemination technique for the species that deposited sperm directly into the uterus. Zoo officials said the population has grown from 18 to more than 700 black-footed ferrets living in the wild.