Zookeeper Breanne Barney overnighted more than 1,000 tadpoles from Como Zoo to Wyoming this week — but not before packing the shipping boxes with ice and securing “LIVE” and “FRAGILE” stickers on the outside.

This cargo was especially precious. The Wyoming toad (or Baxter’s toad) was once feared to be extinct, and it remains among the rarest species in the world.

Como Zoo is one of eight zoos in North America breeding the toads through the Species Survival Plan, a federal program that aims to keep endangered species from extinction by boosting their numbers in captivity. Zoos work with the Association of Zoos and Aquariums and the U.S. Fish and Wildlife Service to breed the animals before releasing them into their native areas.

“We’ve managed to take some big steps to re-establishing this species in the wild, thanks to participants like Como Zoo,” said Val Hornyak, the coordinator for the Wyoming toad’s Species Survival Plan.

The toad’s population, which had once dwindled to 10 in the wild, has rebounded, now numbering in the hundreds in captivity, Hornyak said.

Como Zoo became involved with the program in 2008 and made its first tadpole shipment to Wyoming — the toads’ natural habitat — in 2010. The zoo spends more than $30,000 a year to help save these endangered amphibians, said John Dee, the general curator of the zoo.

“We’re good with amphibians, and they’re fussy animals so you have to be good at it in order to really work with them,” Dee said.

While several of the toads are on display at Como, more than 40 are kept in a closed-off facility, where zookeepers can best control variables such as temperature — especially important for breeding.

The toads must hibernate before breeding begins each spring, and zookeepers coax them into hibernation by dropping the temperature to 34 degrees. Once hibernation ends, the males start singing, helped along by a CD of other toads. The humming sound is all part of the seasonal seduction and helps males attract a mate.

“It’s a beautiful sound, like a pretty chorus,” said Barney, who manages the breeding program.

After the tadpoles have emerged, Barney loads the tiny swimmers into double-sealed bags filled with water and sends them on their way.

“My whole life I’ve wanted to work with endangered species, so when I was given this project, I was beside myself,” Barney said. “I cried.”

The tadpoles arrived safely in Laramie, Wyo., on Wednesday, where Jason Palmer, a biologist with the U.S. Fish and Wildlife Service, picked them up from FedEx and drove them in the front seat of his truck to their new home near Lake Mortenson.

Though it’s hard to get an exact count of toads, Palmer said there are now more than 100 wild toads born from tadpoles like the ones bred at Como Zoo.

“If it wasn’t for the help of the zoos and everyone involved, the population wouldn’t be where it’s at today,” Palmer said.