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During her daily commute to the scientific station, scientist Miriam San José stoops near a shallow water body surrounded by thick plants and retrieves a compact plastic sound device.

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, known by local scientists as an non-native species with consequences that experts are just beginning to understand.

Although teeming with unique wildlife – including centuries-old large turtles, marine lizards, and the well-known birds that inspired 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. Some small tree frogs traveled from continental the mainland to the islands, probably as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been multiple accidental arrivals to the islands, and the amphibians now have a firm presence on two locations: multiple locations.

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

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

They estimated 6,000 frogs in a single pond. "The calculations are still very low," states San José. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's really incredible," says San José.

For the researchers, their nightly vocalizations are useful in determining their existence in far-flung areas, using recorders like the one outside the workplace.

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

"During the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from the island.

"At first it was a surprise, observing the first frogs in the region," says the farmer, who started observing their large numbers about several years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

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

On archipelagos, it is very typical for non-native species to prosper, as they have none of their natural predators. The islands counts 1,645 introduced types, many of which are significantly disrupting the survival of its native ones.

A recent study indicates the invasive frogs are hungry insect consumers, and might be disproportionately eating uncommon insects found only on the islands, or depleting the food sources of the region's rare avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

The island amphibians have exhibited some unusual characteristics, including surviving in slightly salty water, which is rare for amphibians.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a tadpole in her lab for six months.

"We truly don't know this aspect," she says, worried the larvae could be affecting the region's clean water, a very scarce resource in the islands.

Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and slowly increasing the salt content of ponds in without success.

Research suggests spraying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't always safe for other rare Galápagos organisms.

Without solutions to more of the basic questions about their lifestyle and effect, culling the frogs might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she expects 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 difficult to obtain.

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