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On her regular walk to the research facility, biologist Miriam San José crouches near a shallow water body surrounded by dense plants and collects a small plastic audio device.

The device was left there overnight to record the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive threat with effects that scientists are just beginning to understand.

Despite teeming with remarkable wildlife – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's evolutionary theory – the island chain near the coast of Ecuador had long remained free of amphibians.

In the late 1990s, this changed. Some tiny tree frogs made their way from mainland the mainland to the islands, likely as stowaways on transport vessels.

Genetic research indicate that, over the years, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a firm presence on two islands: multiple locations.

The population is growing so quickly 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 Galápagos national park.

When the biologist marked frogs and attempted to find them in the following 10 days, she could find just one tagged frog occasionally, suggesting their populations were massive.

They calculated 6,000 frogs in a single 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' proliferation is evident from the sound chaos they create. "The amount of frogs and the sound – it's truly incredible," says San José.

For the scientists, their nocturnal mating calls are useful in estimating their presence in far-flung areas, using recorders like the one near San José's office.

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

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

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

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, experts still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive species to prosper, as they have none of their enemies. The islands has over sixteen hundred invasive types, many of which are significantly disrupting the safety of its native ones.

A recent study suggests the invasive amphibians are voracious insect consumers, and might be unevenly eating uncommon bugs found exclusively on the archipelago, or depleting the nutrition of the region's uncommon birds, affecting the food chain.

Unusual Traits and Control Challenges

The island frogs have exhibited some atypical characteristics, including living in brackish water, which is uncommon for frogs.

Their metamorphosis stage is also extremely variable, with some larvae becoming frogs very rapidly and others taking a long time: the researcher observed one which stayed as a tadpole in her lab for six months.

"We truly don't know this part," she says, worried the tadpoles could be affecting the islands' clean water, a very scarce resource in the islands.

Methods to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually increasing the salt content of ponds in without success.

Research indicates spraying caffeine – which is highly toxic to frogs – or using electrical methods could assist, but these approaches aren't always secure for other rare island organisms.

Without answers to more of the basic questions about their lifestyle and impact, culling the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she hopes the growing use of eDNA methods and genetic analysis will assist her team understand of the invasive species, funding for the research has been hard to come by.

"Everyone wants to give support for protecting frogs," says San José. "But it's more difficult to find funding for an introduced frog that you might want to control."