The Galápagos Islands Had No Indigenous Amphibians. Until Countless Numbers of Frogs Arrived

During her regular walk to the research facility, biologist the researcher stoops near a shallow pond covered by thick vegetation and retrieves a compact green sound recorder.

The device was left there through the night to record the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an non-native species with effects that experts are starting to understand.

Despite teeming with remarkable wildlife – including ancient giant tortoises, marine iguanas, and the famous finches that inspired Charles Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had long remained devoid of amphibians.

In the late 1990s, this changed. Several tiny tree frogs traveled from mainland the mainland to the archipelago, probably as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong presence on several islands: multiple locations.

The numbers is growing so rapidly that scientists have been struggling to keep track, calculating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the subsequent 10 days, she could locate just one marked frog occasionally, indicating their numbers were enormous.

They estimated 6,000 frogs in a single pond. "The calculations are still very low," says the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

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

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

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

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

"Initially it was a surprise, observing the initial 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 house.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for non-native species to thrive, as they have few of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are seriously affecting the safety of its endemic ones.

A 2020 study indicates the non-native amphibians are voracious insect consumers, and might be unevenly consuming uncommon bugs found exclusively on the islands, or depleting the food sources of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a extended period: San José observed one which remained as a tadpole in her laboratory for six months.

"We truly don't know this aspect," she says, worried the tadpoles could be impacting the islands' clean water, a very scarce commodity in Galápagos.

Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by hand and gradually raising the salinity of ponds in vain.

Studies suggests applying coffee – which is highly toxic to frogs – or using electrocution could assist, but these methods aren't necessarily safe for other rare island organisms.

Lacking solutions to more of the basic questions about their biology and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of environmental DNA techniques and DNA analysis will help her team understand of the invasive species, funding for the research has been difficult to obtain.

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