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During her regular walk to the research facility, scientist Miriam San José stoops near a small pond covered by thick plants and collects a compact plastic audio recorder.

The device was left there overnight to record the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive threat with effects that scientists are starting to understand.

Although teeming with remarkable animals – including ancient large turtles, marine iguanas, and the famous birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained free of frogs and toads.

In the late 1990s, this changed. Some tiny amphibians traveled from continental the mainland to the islands, probably as stowaways on transport vessels.

Genetic research indicate that, over the years, there have been repeated accidental introductions to the archipelago, and the frogs now have a strong foothold on several locations: multiple locations.

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

When San José marked amphibians and attempted to find them in the following 10 days, she could find only a single marked frog occasionally, suggesting their populations were enormous.

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

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the sound disruption they cause. "The number of frogs and the sound – it's really incredible," comments San José.

For the researchers, their nightly vocalizations are helpful in estimating their existence in far-flung areas, using recorders like the one outside the office.

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

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

"At first it was a shock, seeing the first frogs in the region," says Larrea Saltos, who started observing their abundance about three years ago when one jumped on her palm as she was stepping out of her house.

Environmental Consequences Stays Unknown

The sound isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, experts still know limited information about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for invasive organisms to prosper, as they have none of their natural predators. The islands counts 1,645 invasive types, many of which are seriously affecting the survival of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry bug consumers, and might be unevenly consuming rare bugs found only on the archipelago, or depleting the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island frogs have shown some unusual characteristics, including living in slightly salty water, which is rare for amphibians.

Their development process is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a larva in her laboratory for half a year.

"We really don't know this part," she says, worried the tadpoles could be affecting the islands' freshwater, a very scarce resource in Galápagos.

Methods to control the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried collecting significant quantities by manual methods and slowly increasing the salinity of ponds in without success.

Research suggests spraying coffee – which is highly toxic to amphibians – or using electrocution could assist, but these methods aren't necessarily safe for other rare Galápagos species.

Lacking solutions to more of the basic issues about their lifestyle and effect, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will help her team understand of the invader, financial support for the research has been difficult to come by.

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