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

During her regular walk to the research facility, biologist the researcher crouches near a shallow water body covered by thick vegetation and collects a small green sound recorder.

The device was left there overnight to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive threat with effects that scientists are starting to understand.

Despite abounding with remarkable wildlife – including ancient giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs traveled from mainland the mainland to the islands, likely as stowaways on transport vessels.

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

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

When the biologist tagged frogs and attempted to recapture them in the subsequent 10 days, she could locate only a single marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the sound chaos they create. "The number of frogs and the sound – it's really insane," comments the scientist.

For the scientists, their nocturnal vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one near the workplace.

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

"During the rainy period, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

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

Ecological Impact Remains Unclear

The sound 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 land and water environments.

On islands, it is very common for non-native species to prosper, as they have none of their natural predators. The Galápagos counts over sixteen hundred invasive types, many of which are seriously affecting the safety of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry bug consumers, and might be unevenly eating uncommon insects found only on the islands, or reducing the food sources of the islands' rare birds, disrupting the food chain.

Unique Characteristics and Control Challenges

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

Their development stage is also extremely 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 lab for six months.

"We really don't know this part," she says, concerned the tadpoles could be affecting the islands' clean water, a very limited commodity in the islands.

Methods to control the frogs in the beginning of the century were mostly ineffective. Conservation officers tried capturing significant quantities by hand and slowly raising the salinity of lagoons in without success.

Research indicates spraying caffeine – which is highly toxic to frogs – or using electrocution could assist, but these approaches aren't necessarily safe for other rare Galápagos organisms.

Without answers to more of the basic questions about their lifestyle and impact, removing the frogs might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of environmental DNA techniques and DNA examination will assist her group make sense of the invader, funding for the research has been hard to obtain.

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