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On her daily commute to the scientific station, scientist Miriam San José crouches near a shallow pond surrounded by dense vegetation and retrieves a compact plastic audio device.

She had placed there through the night to record the characteristic calls of the Scinax quinquefasciatus, known by Galápagos researchers as an non-native threat with consequences that scientists are just beginning to comprehend.

Although abounding with unique animals – such as centuries-old giant tortoises, marine lizards, and the well-known birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had long remained free of amphibians.

During the 1990s, this changed. Some small tree frogs traveled from continental the mainland to the archipelago, likely as hitchhikers on transport vessels.

DNA studies indicate that, through time, there have been multiple unintentional arrivals to the islands, and the frogs now have a firm presence on several locations: multiple locations.

The numbers is growing so quickly that researchers have been finding it difficult to monitor, estimating numbers in the millions 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, indicating their populations were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very low," says San José. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is evident from the sound chaos they cause. "The number of frogs and the noise – it's really insane," says the scientist.

For the researchers, their nocturnal mating calls are useful in estimating their presence in far-flung areas, using recorders like the one outside San José's workplace.

But nearby agricultural workers say the sounds are so raucous they keep them up at night.

"In the rainy period, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, seeing the first frogs in the region," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

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

On archipelagos, it is very common for invasive species to prosper, as they have none of their enemies. The islands counts over sixteen hundred introduced species, many of which are seriously disrupting the safety of its endemic ones.

A recent research indicates the invasive frogs are hungry bug consumers, and might be disproportionately eating uncommon bugs found only on the archipelago, or reducing the nutrition of the region's uncommon birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The Galápagos amphibians have exhibited some unusual traits, including surviving in slightly salty water, which is uncommon for frogs.

Their metamorphosis process is also highly variable, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for half a year.

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

Methods to curb the amphibians in the beginning of the century were largely ineffective. Park rangers tried collecting significant quantities by hand and gradually raising the salt content of lagoons in vain.

Research suggests applying coffee – which is extremely toxic to frogs – or using electrocution could help, but these methods aren't necessarily secure for other rare island species.

Without solutions to more of the fundamental questions about their biology and effect, culling the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she hopes the increasing use of environmental DNA methods and genetic examination will help her group make sense of the invader, funding for the project has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to manage."