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On her daily walk to the scientific station, scientist the researcher crouches near a shallow water body surrounded by thick vegetation and collects a compact green audio device.

She had placed there overnight to record the characteristic calls of the Fowler's snouted treefrog, recognized by local scientists as an invasive threat with effects that scientists are starting to comprehend.

Despite abounding with unique wildlife – including ancient giant tortoises, marine lizards, and the famous finches that sparked Darwin's evolutionary theory – the island chain near the coast of South America had long remained free of amphibians.

During the 1990s, this shifted. Some small tree frogs made their way from mainland the mainland to the islands, likely as stowaways on cargo ships.

DNA research suggest that, over the years, there have been repeated accidental introductions to the islands, and the frogs now have a strong foothold on two islands: Isabela and Santa Cruz.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, calculating populations in the millions on every island, across urban and farming areas, but also in the protected Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could locate only a single marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says San José. "I'm quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they cause. "The amount of frogs and the noise – it's truly insane," comments the scientist.

For the scientists, their nocturnal vocalizations are helpful in estimating their presence in remote areas, using audio devices like the one outside San José's workplace.

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

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

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

Ecological Impact Remains Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, experts still know very little about its effect on the archipelago's precariously balanced land and water environments.

On archipelagos, it is very typical for non-native species to thrive, as they have none of their natural predators. The Galápagos has 1,645 invasive species, many of which are seriously affecting the survival of its endemic ones.

A 2020 research suggests the non-native amphibians are hungry bug consumers, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or reducing the nutrition of the region's rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also extremely inconsistent, with some tadpoles turning into frogs very quickly and others taking a long time: San José witnessed one which remained as a tadpole in her laboratory for half a year.

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

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by hand and slowly increasing the salt content of lagoons in vain.

Research suggests applying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other rare Galápagos organisms.

Without answers to more of the basic issues about their biology and impact, removing the frogs might not even be the right way to advance, says San José.

Financial Obstacles for Research

While she expects the growing use of eDNA methods and DNA examination will help her team make sense of the invader, financial support for the research has been hard to obtain.

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