Galápagos Lacked Any Indigenous Amphibians. Then Hundreds of Thousands of Frogs Made Their Home

On her regular commute to the research facility, scientist Miriam San José crouches near a small water body surrounded by dense vegetation and collects a small green sound recorder.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native species with consequences that scientists are just beginning to comprehend.

Although abounding with unique animals – such as centuries-old giant tortoises, marine iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained devoid of amphibians.

In the late 1990s, this shifted. Several tiny tree frogs traveled from mainland Ecuador to the islands, likely as hitchhikers on transport vessels.

Genetic research suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a strong presence on two locations: multiple locations.

The population is growing so rapidly that scientists have been struggling to monitor, estimating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the following week and a half, she could locate just one marked frog from time to time, indicating their populations were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is evident from the sound disruption they create. "The number of frogs and the noise – it's truly incredible," comments San José.

For the scientists, their nocturnal mating calls are useful in determining their presence in far-flung areas, using recorders like the one near the office.

But nearby farmers say the sounds are so loud they keep them up at night.

"During the wet season, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, observing the first frogs in the area," says the farmer, who started noticing their abundance about several years ago when one leaped on her hand as she was stepping out of her house.

Ecological Impact Remains Unknown

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, experts still know very little about its impact on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native species to thrive, as they have none of their natural predators. The Galápagos has 1,645 invasive species, many of which are significantly disrupting the survival of its native ones.

A 2020 research indicates the invasive amphibians are voracious insect consumers, and might be unevenly consuming rare insects found exclusively on the archipelago, or reducing the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have exhibited some atypical characteristics, including living in brackish water, which is rare for amphibians.

Their metamorphosis stage is also highly variable, with some tadpoles turning into 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 really don't know this part," she says, concerned the tadpoles could be impacting the islands' clean water, a very scarce resource in Galápagos.

Methods to control the amphibians in the early 2000s were largely ineffective. Park rangers tried capturing significant quantities by manual methods and gradually raising the salt content of lagoons in vain.

Studies suggests applying coffee – which is highly poisonous to frogs – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon Galápagos species.

Without solutions to more of the fundamental questions about their lifestyle and impact, culling the frogs might not even be the correct way to advance, says the biologist.

Funding Challenges for Research

While she expects the growing use of eDNA techniques and genetic analysis will assist her team understand of the invader, funding for the project has been hard to come by.

"Everybody wants to give funding for protecting frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to control."