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During her regular walk to the research facility, biologist Miriam San José crouches near a small water body surrounded by dense plants and collects a compact green sound device.

The device was left there overnight to capture the characteristic calls of the Fowler's snouted treefrog, known by Galápagos researchers as an invasive species with effects that experts are just beginning to understand.

Despite teeming with remarkable animals – including centuries-old large turtles, marine iguanas, and the famous finches that inspired Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had historically been free of frogs and toads.

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

Genetic research indicate that, through time, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a strong presence on two locations: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been struggling to monitor, estimating populations in the millions on every island, across developed and agricultural areas, but also in the protected Galápagos national park.

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

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

Acoustic Chaos and Growing Concerns

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

For the scientists, their nocturnal vocalizations are helpful in estimating their existence in far-flung areas, using audio devices like the one near San José's workplace.

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

"In the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"Initially it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started observing their large numbers about several years ago when one leaped on her palm as she was walking out of her front door.

Ecological Impact Remains Unknown

The noise isn't the primary problem, though. While the amphibians has been in the islands for almost 30 years, scientists still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for invasive organisms to prosper, as they have few of their natural predators. The islands has over sixteen hundred introduced types, many of which are significantly affecting the survival of its native ones.

A recent research indicates the non-native amphibians are hungry insect consumers, and might be unevenly eating rare insects found exclusively on the archipelago, or depleting the food sources of the region's rare birds, disrupting the food chain.

Unusual Traits and Management Difficulties

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

Their development stage is also highly variable, with some tadpoles becoming frogs very rapidly and others taking a long time: San José witnessed one which remained as a tadpole in her lab for half a year.

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

Methods to curb the frogs in the early 2000s were mostly unsuccessful. Park rangers tried collecting significant quantities by hand and slowly raising the salt content of lagoons in vain.

Studies suggests applying coffee – which is extremely toxic to amphibians – or using electrocution could assist, but these approaches aren't necessarily safe for other uncommon island organisms.

Lacking solutions to more of the basic questions about their biology and effect, removing the amphibians might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA methods and genetic analysis will help her group understand of the invader, financial support for the project has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to manage."