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On her regular commute to the research facility, scientist the researcher crouches near a small pond covered by dense vegetation and retrieves a small plastic audio device.

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive species with consequences that experts are starting to understand.

Despite abounding with remarkable wildlife – including centuries-old giant tortoises, swimming lizards, and the well-known finches that sparked Charles Darwin's theory of evolution – the island chain near the shoreline of South America had historically been free of amphibians.

During the 1990s, this shifted. Several small tree frogs made their way from mainland Ecuador to the archipelago, probably as hitchhikers on transport vessels.

DNA research suggest that, over the years, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm foothold on several locations: Isabela and Santa Cruz.

The population is expanding so quickly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the protected Galápagos national park.

When San José marked frogs and attempted to recapture them in the subsequent week and a half, she could find only a single marked frog from time to time, suggesting their numbers were massive.

They calculated 6,000 frogs in a single pond. "Our estimates are still very low," says the researcher. "I am pretty sure there are even more."

Deafening Noise and Growing Concerns

The frogs' abundance is evident from the sound disruption they create. "The amount of frogs and the noise – it's really insane," comments San José.

For the scientists, their nocturnal vocalizations are helpful in estimating their existence in remote areas, using recorders like the one outside the office.

But local agricultural workers say the calls are so raucous they keep them up at night.

"In the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Stays Unknown

The sound isn't the primary problem, though. While the species has been in the islands for nearly 30 years, scientists still know very little about its effect on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for non-native species to prosper, as they have few of their enemies. The Galápagos counts 1,645 introduced species, many of which are significantly affecting the survival of its endemic ones.

A recent research indicates the non-native frogs are hungry insect eaters, and might be unevenly consuming uncommon insects found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

The island frogs have shown some atypical characteristics, including surviving in brackish water, which is rare for amphibians.

Their metamorphosis process is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: the researcher witnessed one which stayed as a tadpole in her laboratory for six months.

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

Techniques to control the frogs in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by hand and gradually raising the salt content of lagoons in without success.

Research indicates spraying coffee – which is extremely poisonous to amphibians – or using electrical methods could help, but these approaches aren't always safe for other uncommon Galápagos species.

Lacking solutions to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the right way to advance, says San José.

Funding Challenges for Research

While she hopes the growing use of eDNA techniques and DNA examination will assist her team make sense of the invader, financial support for the research has been hard to come by.

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