🔗 Share this article

During her daily walk to the research facility, scientist Miriam San José crouches near a shallow water body surrounded by dense plants and collects a compact plastic audio device.

She had placed there through the night to record the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive threat with consequences that experts are just beginning to comprehend.

Although abounding with remarkable wildlife – including ancient giant tortoises, swimming iguanas, and the famous finches that inspired Darwin's evolutionary theory – the island chain off the coast of South America had long remained free of amphibians.

In the late 1990s, this changed. Several small tree frogs made their way from mainland Ecuador to the islands, likely as hitchhikers on transport vessels.

Genetic research indicate that, through time, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm presence on two locations: multiple locations.

The numbers is growing so quickly that researchers have been struggling to keep track, calculating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to find them in the following week and a half, she could locate only a single marked frog occasionally, suggesting their populations were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," states the researcher. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

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

For the researchers, their nightly mating calls are useful in estimating their presence in far-flung areas, using recorders like the one near San José's office.

But local agricultural workers say the calls are so raucous they prevent sleep at night.

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

"At first it was a shock, observing the first frogs in the area," says the farmer, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her front door.

Ecological Impact Remains Unclear

The noise isn't the fundamental 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 land and water environments.

On islands, it is very common for non-native organisms to prosper, as they have none of their natural predators. The Galápagos counts 1,645 introduced types, many of which are seriously disrupting the survival of its native ones.

A 2020 study indicates the non-native amphibians are voracious bug eaters, and might be unevenly eating uncommon insects found only on the islands, or reducing the food sources of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their development stage is also highly variable, with some larvae becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for half a year.

"We truly don't know this part," she says, concerned the larvae could be affecting the region's freshwater, a very scarce resource in Galápagos.

Methods to control the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and slowly raising the salt content of lagoons in vain.

Research indicates spraying coffee – which is highly poisonous to frogs – or using electrocution could assist, but these methods aren't always safe for other rare island species.

Lacking answers to more of the basic issues about their biology and impact, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA methods and DNA examination will assist her team understand of the invader, financial support for the research has been hard to obtain.

"Everyone wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to control."