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During her daily commute to the research facility, biologist Miriam San José crouches near a shallow water body covered by dense vegetation and retrieves a small green audio device.

She had placed there overnight to record the characteristic croaks of the Fowler's snouted treefrog, known by local scientists as an invasive species with effects that experts are starting to understand.

Despite teeming with remarkable animals – such as centuries-old giant tortoises, swimming lizards, and the famous finches that inspired Darwin's theory of evolution – the island chain near the coast of South America had historically been devoid of frogs and toads.

In the late 1990s, this shifted. Some small amphibians traveled from mainland Ecuador to the islands, probably as stowaways on transport vessels.

DNA studies indicate that, through time, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm presence on two locations: multiple locations.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the following 10 days, she could locate just one tagged frog occasionally, indicating their populations were massive.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Growing Concerns

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

For the scientists, their nocturnal mating calls are helpful in determining their existence in remote areas, using recorders like the one outside the workplace.

But local agricultural workers say the calls are so raucous they prevent sleep at night.

"During the wet season, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a surprise, observing the first frogs in the area," says the farmer, who started observing their large numbers about several years ago when one jumped on her palm as she was stepping out of her front door.

Ecological Impact Remains Unclear

The sound isn't the primary problem, however. While the amphibians has been in the islands for nearly 30 years, experts 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 counts over sixteen hundred introduced types, many of which are significantly affecting the survival of its endemic ones.

A recent study suggests the non-native frogs are voracious bug eaters, and might be disproportionately eating rare bugs found exclusively on the islands, or reducing the food sources of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The island frogs have shown some unusual characteristics, including surviving in brackish water, which is uncommon for amphibians.

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

"We really don't know this aspect," she says, worried the larvae could be affecting the region's freshwater, a very limited resource in the islands.

Methods to curb the frogs in the early 2000s were largely ineffective. Park rangers tried collecting large numbers by manual methods and gradually raising the salt content of ponds in vain.

Studies suggests spraying coffee – which is extremely poisonous to amphibians – or using electrical methods could help, but these approaches aren't always safe for other uncommon island organisms.

Lacking solutions to more of the fundamental issues about their biology and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and DNA examination will help her team make sense of the invasive species, funding for the project has been difficult to obtain.

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