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On her daily walk to the scientific station, scientist Miriam San José crouches near a shallow pond covered by thick plants and retrieves a small green audio recorder.

The device was left there overnight to record the distinctive croaks of the Fowler's snouted treefrog, known by local researchers as an invasive species with effects that experts are starting to comprehend.

Despite abounding with unique wildlife – such as centuries-old large turtles, marine iguanas, and the well-known finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had historically been free of amphibians.

In the late 1990s, this shifted. Several small tree frogs traveled from continental the mainland to the islands, probably as hitchhikers on transport vessels.

DNA studies indicate that, through time, there have been multiple accidental arrivals to the islands, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been struggling to keep track, estimating numbers in the millions on every island, across developed and farming areas, but also in the protected Galápagos national park.

When San José tagged amphibians and attempted to find them in the following week and a half, she could find just one marked frog from time to time, suggesting their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am quite certain there are even more."

Deafening Noise and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they create. "The amount of frogs and the sound – it's truly insane," comments the scientist.

For the scientists, their nightly vocalizations are helpful in determining their existence in far-flung areas, using audio devices like the one near San José's workplace.

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

"During the rainy period, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, seeing the initial frogs in the region," says Larrea Saltos, who started observing their abundance about three years ago when one jumped on her palm as she was stepping out of her front door.

Ecological Impact Stays Unknown

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for almost 30 years, experts still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive species to thrive, as they have none of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are significantly affecting the safety of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry bug eaters, and might be disproportionately eating rare bugs found only on the archipelago, or depleting the nutrition of the islands' rare birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

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

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

Techniques to control the amphibians in the beginning of the century were largely ineffective. Park rangers tried capturing significant quantities by hand and gradually raising the salt content of lagoons in without success.

Studies indicates spraying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these methods aren't necessarily safe for other rare island organisms.

Without solutions to more of the basic issues about their lifestyle and impact, culling the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Research

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

"Everyone wants to give support for protecting frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to control."