The Denver Zoo in Colorado reports that it's now home to a very special batch of tadpoles. Before long, the little swimmers will grow into Lake Titicaca frogs – a South American species that's critically endangered. Until now, no institution in the entire northern half of the world has ever bred these amphibians in captivity.

The tiny tadpoles will soon grow into Lake Titicaca frogs. Image: Denver Zoo/Facebook

Lake Titicaca frogs (Telmatobius culeus) are native mostly to the lake they're named for, which straddles the border of Peru and Bolivia. They spend most of their lives at the bottom of the lake, drawing oxygen from the water using their voluminous folds of skin (a trait that has earned them the unflattering nickname "scrotum frogs"). These are large frogs, reaching ten centimetres (four inches) or more from snout to groin.

Over the past 15 years, amidst pollution, habitat loss and hunting, the species has seen an astonishing population decline of around 80%, including a number of devastating mass deaths that have claimed the lives of thousands of frogs. In response, nearby researchers began attempting to breed the frogs in captivity. The first to succeed were at the Huachipa Zoo in Lima, Peru back in 2010.

Scientists at the Denver Zoo spent years supporting this effort, and in November 2015, 20 Lake Titicaca frogs arrived – the first of their species to go to a zoo in North America. According to zookeepers, these amphibians aren't difficult to sustain as long as their environment matches the lake they've adapted to.

According to their keepers, the new arrivals are doing just fine. Image: Denver Zoo/Facebook

"Currently, Denver Zoo is the only institution in the northern hemisphere to house this critically endangered species," the zoo reported on Facebook.

Apparently, the frogs are plenty comfortable, since they have now done what animals do best – made more animals! Lake Titicaca frogs often lay hundreds of eggs at a time, and on Valentine's Day this year, the Denver Zoo went from having 20 individuals to having around 200. Mazel tov!

The team reports that the tadpoles are still doing quite well. They currently live in the zoo's Tropical Discovery exhibit, alongside exotic fish, reptiles and amphibians, including the newborns' parents.