Galápagos Had No Native Amphibians. Until Countless Numbers of Frogs Arrived

On her daily walk to the scientific station, scientist the researcher crouches near a shallow pond covered by dense vegetation and collects a compact plastic audio recorder.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive species with consequences that experts are starting to understand.

Although abounding with unique animals – such as centuries-old giant tortoises, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained free of amphibians.

In the late 1990s, this shifted. Several small tree frogs traveled from continental Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research indicate that, over the years, there have been repeated accidental introductions to the archipelago, and the frogs now have a firm foothold on several locations: Isabela and Santa Cruz.

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

When the biologist marked amphibians and attempted to find them in the subsequent 10 days, she could locate only a single tagged frog occasionally, suggesting their populations were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the sound disruption they create. "The number of frogs and the noise – it's really insane," says San José.

For the researchers, their nightly vocalizations are useful in determining their presence in remote areas, using recorders like the one outside San José's office.

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

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

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

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the islands for nearly three decades, experts still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native species to prosper, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are seriously disrupting the safety of its native ones.

A recent study indicates the invasive frogs are voracious insect eaters, and might be disproportionately consuming rare bugs found only on the archipelago, or reducing the nutrition of the islands' rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have shown some unusual traits, including living in slightly salty water, which is rare for amphibians.

Their development process is also highly variable, with some tadpoles turning into frogs very quickly and others taking a long time: San José observed one which remained as a tadpole in her laboratory for six months.

"We truly don't know this part," she says, worried the tadpoles could be affecting the region's freshwater, a very scarce commodity in the islands.

Techniques to curb the amphibians in the early 2000s were mostly ineffective. Park rangers tried collecting large numbers by hand and gradually increasing the salinity of lagoons in without success.

Studies indicates spraying coffee – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily safe for other rare island species.

Lacking answers to more of the fundamental questions about their biology and effect, culling the amphibians might not even be the right way to proceed, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and genetic analysis will assist her team understand of the invasive species, financial support for the project has been hard to obtain.

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