Galápagos Had No Native Amphibians. Until Hundreds of Thousands of Amphibians Made Their Home

During her daily walk to the research facility, scientist the researcher crouches near a shallow pond surrounded by dense vegetation and retrieves a compact plastic audio recorder.

She had placed there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by local scientists as an invasive threat with effects that experts are just beginning to understand.

Although abounding with remarkable wildlife – such as ancient large turtles, marine lizards, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained free of amphibians.

During the 1990s, this changed. Several tiny tree frogs made their way from mainland the mainland to the islands, probably as stowaways on transport vessels.

Genetic studies indicate that, over the years, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm foothold on two locations: multiple locations.

The numbers is expanding so quickly that researchers have been finding it difficult to keep track, calculating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to recapture them in the following week and a half, she could locate just one marked frog from time to time, suggesting their numbers were massive.

They calculated six thousand frogs in a single pond. "Our estimates are still very low," states San José. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the acoustic disruption they create. "The amount of frogs and the sound – it's truly incredible," says the scientist.

For the scientists, their nocturnal vocalizations are useful in estimating their existence in remote areas, using audio devices like the one outside San José's office.

But nearby farmers say the calls are so raucous they prevent sleep at night.

"In the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

"At first it was a surprise, seeing the first frogs in the region," says the farmer, who started observing their large numbers about several years ago when one jumped on her palm as she was stepping out of her house.

Ecological Impact Stays Unknown

The noise isn't the primary problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the archipelago's precariously balanced land and water environments.

On archipelagos, it is very typical for non-native species to thrive, as they have none of their enemies. The islands has over sixteen hundred invasive species, many of which are seriously affecting the survival of its native ones.

A 2020 study suggests the invasive frogs are hungry bug consumers, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or reducing the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have shown some unusual traits, including living in brackish water, which is uncommon for amphibians.

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher observed one which remained as a tadpole in her laboratory for half a year.

"We truly don't know this part," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited resource in Galápagos.

Techniques to control the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually raising the salinity of ponds in without success.

Studies indicates spraying coffee – which is highly toxic to frogs – or using electrocution could assist, but these approaches aren't always safe for other uncommon Galápagos species.

Lacking solutions to more of the fundamental issues about their lifestyle and impact, removing the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and genetic analysis will assist her group make sense of the invader, financial support for the project has been difficult to come by.

"Everyone wants to give funding for preserving frogs," says the researcher. "But it's harder to find funding for an introduced frog that you might want to control."