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THE ZOOLOGIST ISSUE 17 | SPRING 2025 | EXCLUSIVELY FOR ZSL FELLOWS
Over 50 southern Darwin's frogs (Rhinoderma darwinii) made the journey from southern Chile to their new home at London Zoo
VOYAGE TO SAVE FROG FIRST DESCRIBED ON HMS BEAGLE
Rescue mission to Chile returns to London Zoo with Darwin’s frog recovery population
I
n late 2024, scientists from ZSL’s Institute of Zoology embarked on a rescue mission to Chile’s Parque Tantauco, bringing some of the last remaining southern Darwin’s frogs into human care. The successful expedition returned with 53 frogs, all now cared for by amphibian experts in a bio-secure facility at London Zoo. The expedition was prompted by the arrival of chytrid fungus on Isla Grande de Chiloé, home to Parque Tantauco, and the subsequent rapid decline of frog populations. Since the identification of amphibian chytrid in the 1990s, by a team of researchers that included ZSL, the fungus has been linked to the extinction in the wild of 90 amphibian species and the decline of over 500 worldwide. The southern Darwin’s frog is highly threatened and evolutionarily unique, making it a high priority for conservation intervention. It is one of only two species of amphibian where the males raise their tadpoles in their vocal sac; the other species, the northern Darwin’s frog, was last seen in 1981 and is already considered possibly extinct. Both are named for ZSL Fellow Charles Darwin, who collected and recorded the frogs during his 183136 expedition aboard the HMS Beagle.
That would all change in 2023, when an expedition revealed chytrid’s arrival. “We monitor two sub-populations of frogs in the park, and we found chytrid present on around a third of frogs in both populations. However, the abundance of the frogs themselves hadn’t dropped, so it’s possible our visit was only shortly after chytrid’s arrival,” explains Andrés Valenzuela-Sánchez, Research Fellow at the Institute of Zoology. Two subsequent visits in early 2024 would paint a much darker picture, says Andrés. “One of our two study populations had completely disappeared, and just a handful of frogs remained in the other. “We surveyed over 28 plots of forest in Tantauco’s southern sector, Inio, and found only 11 frogs,” says Andrés. Further analyses indicate that over 1,300 Darwin’s frogs died in a single year following the invasion of the chytrid fungus in Parque Tantauco in 2023. It was only on the last day that the team had some luck. Miraculously, on one final trek into a deep area of jungle, the team found a single, healthy population of southern Darwin’s frogs, untouched by chytrid.
Chytrid arrives on Chiloé
A lifeline at London Zoo
ZSL and its partners have been monitoring southern Darwin’s frogs in Parque Tantauco on Chiloé since 2010. The protected area was home to the largest known population of the species and, unlike other areas of Chiloé and on the Chilean mainland, remained chytrid free until at least 2022.
Having learned of the incredible scale of destruction wreaked by chytrid, Andrés and his colleagues began planning a rescue attempt. It was from the remote, healthy population found on that final day – possibly the last healthy one on the island – that the frogs now safely being cared for at London Zoo originate.
The rescue attempt brought together a huge collaboration of organisations in support of the frog – including local NGO Ranita de Darwin, Fundación Parque Tantauco, Universidad Andrés Bello, Zoo Leipzig and the Chilean Government. “Getting the permits to rescue the frogs was not easy,” says Andrés, “but having such a huge backing helped us immensely.” In the end, permits were issued just 10 days before the expedition was due to take place. Once in Chile, the team spent five days collecting frogs. After checking the frogs were chytrid-free, they began a two-day journey by boat, plane and car to London. Their numbers have since swollen to 86, thanks to the 12 adult male frogs who successfully brought their young to London in their vocal sacs. The frogs will form a core part of a recovery population of southern Darwin’s frogs, that Andrés hopes will feed a reintroduction back to Parque Tantauco when the time is right. Similar rescue populations will also be set up at Universidad de Concepción in Chile and potentially at Zoo Leipzig in Germany, while Andrés’ research into the causes and possible solutions to chytrid will contribute to the global movement of scientists working to bring amphibian extinctions to a halt. Watch our short documentary about the Darwin's frog rescue, Andrés Valenzuela-Sánchez, A Leap of Hope, at Research Fellow, ZSL’s Institute of Zoology ZSL.org/DarwinRescue