On December 4, 2003, the Saint Louis Zoo shipped five-day-old tadpoles, the endangered Puerto Rican crested toad, back to Puerto Rico for reintroduction to pools in Guanica State Forest.

In St. Louis, the Herpetarium staff produced a “bumper crop” of 6,500 tadpoles of this endangered amphibian. The staff put the tadpoles in bags of water and pure oxygen for their big flight south. The shipment was then picked up by U.S. Fish & Wildlife Service at the airport in Puerto Rico and driven directly to the release site, where about 20,000 tadpoles were released last October.

This is the second time the Saint Louis Zoo has participated in a tadpole shipment to Puerto Rico. To precondition a group of adult toads for breeding, the Zoo staff used a circulating rain shower, then injected several pairs of toads with hormones during the amplexus stage of mating to increase their fertility. The toads laid strings of eggs, which hatched two days later.

The Puerto Rican crested toad is the only toad native to Puerto Rico. Once common, human activity led to its dramatic decline. Besides invading more and more “toad real estate,” humans have introduced dogs, cats, mongoose, rats and a superior competitor, the giant marine toad, which have all played a part in reducing the crested toads’ chances for survival.

Previously thought to be extinct, six toads were collected for captive breeding in 1982. At that time, it was estimated that less than 200 crested toads remained. Since then, the crested toad has been incorporated into the American Zoo and Aquarium Association’s (AZA) Species Survival Plan.