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During her daily commute to the scientific station, scientist the researcher crouches near a small water body covered by thick plants and retrieves a compact plastic audio recorder.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with effects that experts are starting to comprehend.

Despite abounding with unique wildlife – such as centuries-old giant tortoises, marine lizards, and the well-known finches that sparked Darwin's theory of evolution – the island chain off the coast of South America had historically been devoid of amphibians.

During the 1990s, this shifted. Several small tree frogs traveled from continental Ecuador to the archipelago, probably as stowaways on transport vessels.

DNA research indicate that, over the years, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong presence on two locations: Isabela and Santa Cruz.

The numbers is expanding so quickly that researchers have been finding it difficult to keep track, estimating numbers in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the subsequent 10 days, she could find just one marked frog from time to time, suggesting their numbers were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nightly vocalizations are helpful in determining their presence in remote areas, using audio devices like the one near San José's office.

But nearby agricultural workers say the calls are so loud they prevent sleep at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

"Initially it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one jumped on her palm as she was stepping out of her house.

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, however. While the species has been in the Galápagos for nearly three decades, experts still know very little about its effect on the islands' delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos counts over sixteen hundred invasive species, many of which are seriously affecting the survival of its native ones.

A 2020 study indicates the invasive amphibians are voracious bug eaters, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or reducing the food sources of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Control Challenges

The Galápagos amphibians have exhibited some unusual traits, including living in slightly salty water, which is rare for amphibians.

Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very quickly and others taking a extended period: San José witnessed one which remained as a larva in her laboratory for half a year.

"We really don't know this aspect," she says, worried the larvae could be impacting the islands' clean water, a very limited resource in Galápagos.

Methods to curb the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried collecting significant quantities by manual methods and slowly raising the salinity of lagoons in without success.

Studies suggests applying coffee – which is highly toxic to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon island species.

Lacking solutions to more of the basic issues about their biology and effect, culling the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she expects the growing use of environmental DNA methods and DNA examination will help her team understand of the invasive species, funding for the research has been hard to obtain.

"Everyone wants to give support for protecting frogs," says the researcher. "But it's harder to find financial backing for an introduced frog that you might want to control."