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On her regular walk to the scientific station, biologist Miriam San José stoops near a small water body covered by dense vegetation and retrieves a compact green audio device.

The device was left there through the night to record the distinctive croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with effects that experts are just beginning to understand.

Despite teeming with remarkable wildlife – such as ancient giant tortoises, marine iguanas, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had historically been devoid of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs traveled from continental Ecuador to the archipelago, probably as stowaways on cargo ships.

DNA studies indicate that, through time, there have been repeated accidental introductions to the archipelago, and the amphibians now have a strong presence on several islands: multiple locations.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, calculating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation natural reserve.

When San José tagged frogs and attempted to recapture them in the following 10 days, she could find only a single tagged frog from time to time, indicating their numbers were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very low," states the researcher. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly mating calls are helpful in determining their presence in far-flung areas, using recorders like the one near the office.

But local farmers say the calls are so loud they keep them up at night.

"During the rainy period, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the species has been in the Galápagos for nearly three decades, experts still know very little about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for invasive species to thrive, as they have few of their natural predators. The islands has over sixteen hundred invasive types, many of which are seriously disrupting the survival of its endemic ones.

A recent study suggests the invasive amphibians are hungry bug consumers, and might be disproportionately consuming rare bugs found only on the islands, or depleting the nutrition of the islands' rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for half a year.

"We really don't know this aspect," she says, worried the larvae could be affecting the region's freshwater, a very limited commodity in Galápagos.

Methods to control the frogs in the early 2000s were largely unsuccessful. Park rangers tried collecting significant quantities by manual methods and gradually increasing the salt content of ponds in without success.

Studies indicates applying coffee – which is extremely poisonous to amphibians – or using electrocution could assist, but these methods aren't necessarily secure for other rare island species.

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

Financial Obstacles for Study

While she hopes the growing use of environmental DNA methods and genetic examination will assist her team understand of the invader, funding for the project has been difficult to obtain.

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