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During her daily commute to the scientific station, scientist Miriam San José crouches near a small water body surrounded by thick plants and collects a compact plastic audio device.

The device was left there overnight to record the characteristic croaks of the Fowler's snouted treefrog, known by local researchers as an invasive species with effects that scientists are just beginning to understand.

Despite abounding with remarkable wildlife – such as centuries-old large turtles, swimming iguanas, and the famous finches that sparked Darwin's theory of evolution – the island chain off the coast of South America had historically been free of amphibians.

During the 1990s, this changed. Several small amphibians made their way from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.

Genetic studies indicate that, over the years, there have been multiple unintentional introductions to the islands, and the amphibians now have a strong foothold on two islands: 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 urban and farming areas, but also in the conservation Galápagos national park.

When San José tagged frogs and attempted to find them in the following 10 days, she could locate just one marked frog from time to time, suggesting their populations were massive.

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

Acoustic Chaos and Growing Concerns

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

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

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

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

"At first it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started noticing their abundance about three years ago when one leaped 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 species has been in the Galápagos for nearly 30 years, scientists still know limited information about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for invasive species to thrive, as they have few of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are seriously disrupting the survival of its endemic ones.

A 2020 study suggests the non-native frogs are hungry bug eaters, and might be unevenly eating uncommon insects found only on the archipelago, or depleting the food sources of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

The island amphibians have shown some atypical characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for half a year.

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

Techniques to control the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and gradually increasing the salt content of lagoons in without success.

Research indicates spraying caffeine – which is highly poisonous to amphibians – or using electrical methods could help, but these approaches aren't necessarily secure for other rare island species.

Without solutions to more of the fundamental issues about their lifestyle and impact, removing the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she hopes the increasing use of eDNA methods and genetic analysis will help her group make sense of the invader, financial support for the research has been difficult to come by.

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