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On her regular commute to the research facility, biologist Miriam San José stoops near a shallow water body covered by thick vegetation and collects a compact plastic sound device.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by local researchers as an invasive species with effects that experts are starting to comprehend.

Although teeming with unique wildlife – including ancient giant tortoises, marine iguanas, and the well-known finches that sparked Charles Darwin's evolutionary theory – the island chain off the coast of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs traveled from continental the mainland to the islands, probably as hitchhikers on transport vessels.

Genetic studies suggest that, over the years, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong foothold on two islands: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been finding it difficult to monitor, estimating numbers in the millions on every island, across developed and farming areas, but also in the conservation Galápagos national park.

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

They estimated six thousand frogs in a single pond. "Our estimates are still very low," says the researcher. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the acoustic disruption they cause. "The number of frogs and the sound – it's really insane," says the scientist.

For the scientists, their nocturnal mating calls are helpful in determining their presence in remote areas, using audio devices like the one near the workplace.

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

"During the wet season, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

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

Environmental Consequences Stays Unclear

The sound isn't the primary problem, however. While the species has been in the islands for nearly three decades, experts still know very little about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very common for non-native species to thrive, as they have none of their natural predators. The islands counts over sixteen hundred invasive types, many of which are seriously disrupting the survival of its endemic ones.

A 2020 study indicates the invasive frogs are hungry insect eaters, and might be unevenly eating uncommon insects found only on the islands, or reducing the food sources of the islands' uncommon birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

The island frogs have exhibited some unusual traits, including living in brackish water, which is rare 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 observed one which stayed as a tadpole in her laboratory for half a year.

"We really don't know this part," she says, worried the larvae could be affecting the islands' clean water, a very scarce commodity in Galápagos.

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried collecting significant quantities by hand and slowly raising the salinity of ponds in vain.

Research suggests spraying caffeine – which is highly poisonous to frogs – or using electrocution could assist, but these approaches aren't always secure for other rare Galápagos organisms.

Without solutions to more of the fundamental issues about their lifestyle and impact, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA methods and DNA examination will assist her group make sense of the invasive species, financial support for the project has been hard to obtain.

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