Endangered frogs born at London zoo after rescue mission in Chile

Dozens of endangered froglets have been born at London zoo after conservationists launched an emergency mission to rescue members of the species from a remote national park in Chile.

Researchers rushed to Tantauco Park on the southern tip of Chiloé Island after tests confirmed that the lethal chytrid fungus had reached the nature reserve and threatened to wipe out some of the last remaining populations of Darwin’s frogs.

The island was regarded as a sanctuary for the endangered species but monitoring in 2023 revealed a 90% crash in numbers due to chytrid fungus, which has been called the most devastating infectious animal disease ever documented.

“We realised the situation was really, really bad,” said Dr Andrés Valenzuela-Sánchez, a research fellow at the Zoological Society of London (ZSL). “We rapidly decided we needed to do something; we needed to do an emergency rescue.”

Chytrid fungus has spread around the world in the past 30 years with catastrophic consequences for amphibians. It has killed off at least 90 species and affected hundreds more. Darwin’s frogs, named after the Victorian naturalist who discovered them in 1834, are highly susceptible to the disease and die within weeks of becoming infected.

On a five-day expedition to the park in October last year, the rescue team collected 55 Darwin’s frogs. Some were located after local guides mimicked the amphibians’ calls, prompting responses from the tiny creatures.

Shortly after capturing the frogs, which weigh only 2g fully grown, the team realised that 11 males were carrying young. Darwin’s frogs have an unusual reproductive cycle. The males fertilise eggs that females lay on the forest floor and two to three weeks they later collect them in their mouths where they pass into a vocal sac for brooding. The tadpoles slowly metamorphose and are later born as froglets.

To check whether the frogs were infected with fungus, skin swabs were sent to a laboratory in Chile’s capital, Santiago. Tests identified two contaminated frogs. The remaining 53 were cleared for the approximately 8,000-mile (13,000km) journey to London by boat, plane and van.

The frogs arrived in good health and were transferred to a newly built biosecure room at the zoo that mimics the cool temperature, rainfall, lighting and foliage of the frogs’ natural habitat. Once settled, the males that had been carrying tadpoles on capture released 33 froglets into the enclosure. Each measured about 5mm long.

“We have the founders, the first adults, and now we have this first generation of offspring born at the zoo,” Valenzuela-Sánchez told the Guardian. The researchers now hope to breed the frogs and study potential treatments for chytrid fungus that would allow the amphibians to be returned home.

The rescue mission was recorded for ZSL by the wildlife film-maker Paul Glynn, whose documentary A Leap of Hope will premiere on YouTube at 6pm GMT on Monday.