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On her daily walk to the research facility, biologist Miriam San José crouches near a small pond covered by thick vegetation and collects a compact plastic audio device.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with consequences that scientists are just beginning to comprehend.

Despite teeming with remarkable wildlife – including centuries-old giant tortoises, swimming iguanas, and the famous birds that sparked Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several small amphibians traveled from mainland Ecuador to the islands, probably as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been multiple accidental introductions to the archipelago, and the amphibians now have a firm presence on two locations: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been struggling to monitor, estimating populations in the millions on each island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to find them in the subsequent 10 days, she could find just one marked frog from time to time, indicating their populations were enormous.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very low," states San José. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the acoustic disruption they cause. "The amount of frogs and the sound – it's truly incredible," says the scientist.

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

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

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

"Initially it was a shock, observing the first 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 house.

Ecological Impact Remains Unclear

The sound isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly 30 years, scientists still know limited information about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive organisms to thrive, as they have none of their natural predators. The Galápagos counts 1,645 introduced species, many of which are significantly disrupting the survival of its endemic ones.

A recent research indicates the invasive frogs are hungry insect eaters, and might be unevenly eating rare insects found exclusively on the archipelago, or depleting the food sources of the region's rare birds, affecting the food chain.

Unique Characteristics and Control Challenges

The island frogs have exhibited some unusual characteristics, including surviving in brackish water, which is rare for frogs.

Their development process is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a long time: San José witnessed one which stayed as a larva in her lab for six months.

"We truly don't know this part," she says, concerned the larvae could be affecting the islands' clean water, a very scarce commodity in Galápagos.

Techniques to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried collecting significant quantities by manual methods and gradually raising the salinity of ponds in without success.

Research indicates spraying coffee – which is highly toxic to amphibians – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos organisms.

Lacking answers to more of the basic questions about their biology and effect, removing the frogs 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 methods and genetic examination will help her team understand of the invader, financial support for the project has been hard to obtain.

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