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On her daily walk to the research facility, biologist Miriam San José crouches near a small water body covered by thick plants and retrieves a compact green sound device.

The device was left there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local researchers as an invasive threat with consequences that experts are starting to comprehend.

Despite abounding with unique wildlife – such as ancient giant tortoises, swimming iguanas, and the well-known birds that inspired Charles Darwin's evolutionary theory – the island chain off the coast of South America had long remained devoid of amphibians.

During the 1990s, this changed. Several tiny amphibians traveled from mainland the mainland to the archipelago, likely as hitchhikers on cargo ships.

DNA research indicate that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong foothold on several islands: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to monitor, calculating populations in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When San José tagged frogs and attempted to find them in the following week and a half, she could locate only a single tagged frog from time to time, indicating their numbers were enormous.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nocturnal mating calls are useful in estimating their presence in remote areas, using audio devices like the one outside San José's office.

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

"During the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from the island.

"Initially it was a shock, observing the initial frogs in the area," says the farmer, who started observing their abundance about several years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Remains Unknown

The sound isn't the primary problem, though. While the amphibians has been in the Galápagos for almost three decades, experts still know limited information about its effect on the archipelago's delicately balanced land and water environments.

On islands, it is very common for invasive organisms to prosper, as they have few of their natural predators. The Galápagos has 1,645 introduced species, many of which are significantly disrupting the safety of its endemic ones.

A recent research indicates the invasive amphibians are hungry bug consumers, and might be disproportionately consuming uncommon bugs found only on the islands, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Control Challenges

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

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

"We truly don't know this aspect," she says, worried the tadpoles could be impacting the region's freshwater, a very scarce commodity in the islands.

Techniques to control the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and gradually increasing the salt content of ponds in vain.

Studies indicates spraying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these approaches aren't necessarily safe for other rare Galápagos organisms.

Lacking solutions to more of the fundamental issues about their biology and effect, removing the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the increasing use of environmental DNA techniques and genetic analysis will assist her team make sense of the invader, financial support for the project has been difficult to come by.

"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."