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During her regular commute to the scientific station, scientist the researcher stoops near a small pond surrounded by dense vegetation and retrieves a compact plastic sound device.

She had placed there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by local scientists as an invasive threat with effects that experts are just beginning to understand.

Although abounding with unique animals – such as ancient giant tortoises, swimming lizards, and the famous birds that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained devoid of frogs and toads.

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

Genetic studies indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been finding it difficult to monitor, estimating populations in the millions on each island, across developed and agricultural areas, but also in the protected Galápagos national park.

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

They estimated six thousand frogs in a solitary pond. "The calculations are still very conservative," says San José. "I'm quite certain there are even more."

Deafening Noise and Growing Concerns

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

For the researchers, their nightly mating calls are helpful in estimating their presence in remote areas, using recorders like the one near the workplace.

But local farmers say the sounds 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 shock, seeing the first frogs in the area," says Larrea Saltos, who started observing their large numbers about several years ago when one leaped on her palm as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, however. While the species has been in the islands for almost three decades, scientists still know very little about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for non-native species to thrive, as they have few of their natural predators. The Galápagos has 1,645 introduced species, many of which are seriously disrupting the safety of its native ones.

A 2020 study indicates the non-native frogs are voracious insect consumers, and might be disproportionately eating rare insects found only on the islands, or reducing the nutrition of the region's rare birds, affecting the food chain.

Unique Characteristics and Control Challenges

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

Their development process is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a long time: San José observed one which remained as a larva in her laboratory for half a year.

"We really don't know this part," she says, worried the larvae could be impacting the region's freshwater, a very limited resource in the islands.

Methods to curb the frogs in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by manual methods and slowly increasing the salinity of lagoons in vain.

Studies indicates applying caffeine – which is highly poisonous to frogs – or using electrocution could assist, but these methods aren't always secure for other uncommon Galápagos organisms.

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

Funding Challenges for Study

While she hopes the growing use of environmental DNA techniques and DNA analysis will assist her group understand of the invader, funding for the research has been difficult to obtain.

"Everyone wants to give funding for protecting frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to manage."