People on a series of redeye flights from San Francisco to Puerto Rico in late October "had no idea they were flying with 4,000 highly endangered toads," says Adam Fink, the zoological manager of the Oakland Zoo.

And rather than take up seat space or overhead bins, the tadpoles were stashed away in an insulated container in the plane's hold.

The tadpoles represent hope for the critically endangered Puerto Rican crested toad (Peltophryne lemur), the only toad native to Puerto Rico, and a unique species that had been thought extinct for much of the 20th century. Preferring arid or semi-arid areas of Karst limestone, the toads are identifiable by their unique head crests.

On October 20, the tadpoles were unpacked and