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

The device was left there through the night to capture the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an invasive threat with consequences that scientists are starting to comprehend.

Although teeming with remarkable wildlife – including centuries-old large turtles, swimming lizards, and the well-known birds that sparked Darwin's evolutionary theory – the Galápagos archipelago near the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this changed. Several small tree frogs made their way from continental Ecuador to the islands, probably as hitchhikers on transport vessels.

DNA research suggest that, through time, there have been repeated accidental introductions to the islands, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

The numbers is growing so rapidly that scientists have been finding it difficult to monitor, estimating numbers in the hundreds of thousands on every island, across developed and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent week and a half, she could locate only a single marked frog occasionally, indicating their numbers were massive.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly mating calls are useful in determining their presence in remote areas, using audio devices like the one near the office.

But local agricultural workers say the calls are so raucous they keep them up at night.

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

"At first it was a surprise, observing the first frogs in the region," says the farmer, who started noticing their abundance about several years ago when one jumped on her hand as she was walking out of her house.

Environmental Consequences Stays Unknown

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 impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive species to prosper, as they have none of their natural predators. The Galápagos has over sixteen hundred introduced species, many of which are seriously affecting the safety of its endemic ones.

A recent study suggests the invasive amphibians are hungry bug consumers, and might be unevenly consuming rare insects found only on the archipelago, or reducing the nutrition of the region's rare avian species, affecting the food chain.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José witnessed one which stayed as a larva in her laboratory for six months.

"We really don't know this part," she says, concerned the larvae could be impacting the region's freshwater, a very scarce resource in Galápagos.

Methods to control the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting large numbers by manual methods and gradually raising the salinity of ponds in vain.

Studies suggests applying caffeine – which is highly poisonous to amphibians – or using electrical methods could assist, but these approaches aren't always safe for other uncommon Galápagos organisms.

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

Financial Obstacles for Research

While she hopes the growing use of eDNA methods and DNA examination will assist her team make sense of the invasive species, funding for the project has been difficult to obtain.

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