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During her regular commute to the scientific station, scientist Miriam San José stoops near a small pond covered by dense vegetation and retrieves a small green audio device.

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

Despite abounding with remarkable wildlife – including ancient large turtles, swimming lizards, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had historically been devoid of frogs and toads.

During the 1990s, this changed. Some small amphibians traveled from continental the mainland to the islands, likely as stowaways on transport vessels.

Genetic research suggest that, over the years, there have been multiple accidental introductions to the archipelago, and the amphibians now have a strong presence on several locations: multiple locations.

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

When the biologist marked frogs and attempted to recapture them in the subsequent week and a half, she could find just one marked frog from time to time, indicating their populations were enormous.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very low," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' abundance is clear from the acoustic disruption they create. "The amount of frogs and the noise – it's really insane," says the scientist.

For the scientists, their nocturnal mating calls are helpful in estimating their existence in remote areas, using audio devices like the one outside the office.

But nearby agricultural workers say the calls are so loud they keep them up at night.

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

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

Environmental Consequences Remains Unclear

The sound isn't the primary problem, though. While the species has been in the islands for almost 30 years, experts still know very little about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive organisms to prosper, as they have none of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are significantly disrupting the survival of its endemic ones.

A 2020 research suggests the non-native frogs are voracious bug consumers, and might be unevenly consuming uncommon insects found only on the archipelago, or reducing the nutrition of the islands' rare birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have exhibited some atypical traits, including living in brackish water, which is uncommon for amphibians.

Their development stage is also highly variable, with some tadpoles turning into frogs very rapidly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory 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 resource in Galápagos.

Methods to curb the amphibians in the beginning of the century were mostly ineffective. Conservation officers tried capturing large numbers by manual methods and gradually raising the salinity of ponds in without success.

Studies indicates applying caffeine – which is extremely poisonous to frogs – or using electrocution could assist, but these approaches aren't necessarily safe for other rare Galápagos organisms.

Without answers to more of the basic questions about their biology and impact, culling the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and genetic analysis will help her group make sense of the invasive species, funding 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."