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On her daily commute to the research facility, biologist Miriam San José stoops near a shallow water body covered by dense plants and collects a small plastic sound device.

The device was left there through the night to capture the characteristic calls of the Fowler's snouted treefrog, known by Galápagos scientists as an non-native threat with consequences that experts are starting to comprehend.

Despite teeming with remarkable animals – including ancient large turtles, swimming iguanas, and the well-known birds that inspired Charles Darwin's theory of evolution – the island chain near the coast of South America had historically been devoid of amphibians.

During the 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the islands, likely as stowaways on cargo ships.

DNA studies suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm presence on several locations: multiple locations.

The numbers is growing so quickly that researchers have been finding it difficult to keep track, calculating populations in the millions on every island, across urban and agricultural areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to recapture them in the subsequent 10 days, she could find only a single tagged frog occasionally, suggesting their numbers were enormous.

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

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the sound chaos they cause. "The number of frogs and the noise – it's really incredible," comments the scientist.

For the scientists, their nightly mating calls are helpful in estimating their presence in remote areas, using audio devices like the one near the office.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

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

"Initially it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Remains Unclear

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

On islands, it is very typical for non-native organisms to prosper, as they have none of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are seriously affecting the safety of its native ones.

A recent study indicates the invasive amphibians are hungry bug consumers, and might be unevenly eating rare bugs found only on the archipelago, or reducing the nutrition of the region's rare birds, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have shown some atypical traits, including surviving in brackish water, which is uncommon for frogs.

Their metamorphosis stage is also extremely variable, with some larvae becoming frogs very quickly and others taking a long time: the researcher observed one which stayed as a tadpole in her lab for half a year.

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

Techniques to control the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried collecting large numbers by manual methods and gradually raising the salinity of ponds in without success.

Studies suggests spraying caffeine – which is highly toxic to amphibians – or using electrical methods could help, but these approaches aren't necessarily safe for other rare Galápagos species.

Lacking solutions to more of the basic issues about their lifestyle and impact, removing the frogs might not even be the right way to advance, says San José.

Funding Challenges for Research

While she hopes the increasing use of environmental DNA techniques and DNA examination will help her team understand of the invader, funding for the research has been hard to obtain.

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