Soaring species: Endangered baby toads fly to Puerto Rico

More than 4,000 wiggling tadpoles conceived via wine fridges in California and then packed in a passenger plane headed to Puerto Rico on Thursday as part of a program to re-establish a technicolor native toad once thought extinct.

The Oakland Zoo since 2014 has taken part in a campaign by North American zoos breeding the critically endangered Puerto Rico crested toad for release into protected ponds on the island, their ancestral home.

Zoological manager Adam Fink was using flight-tracking apps Thursday to monitor the 4,069-week-old tadpoles on their layover in Atlanta. They were traveling in double-bagged baggies topped up with oxygen.

"Every single tadpole is important," Fink said.

He and others had spent the day before the flight netting, packing and counting the tadpoles, bred from two pairs of the 19 Puerto Rico crested toads at the zoo.

The toads—their hides a mix of brown, red, green and yellow—thrived on Puerto Rico until sugar growers introduced a foreign toad they hoped would eat pests that feed on sugar cane. The introduced toad ate the native toad's young and took over its habitat, while human development eliminated much of the native toad's range.

Biologists thought the crested toad had gone extinct, until a few survivors were found in 1984 and became the basis of the breeding program.

At the Oakland Zoo, breeders use wine fridges to cool the adult toads to a state near hibernation, inducing them to breed, Fink said. This is the second year the toads have been flown from the zoo to Puerto Rico, traveling in the cargo holds of commercial airlines.

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