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During her regular walk to the scientific station, scientist the researcher crouches near a shallow pond covered by dense vegetation and collects a compact plastic sound device.

The device was left there through the night to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive threat with consequences that experts are starting to comprehend.

Although abounding with remarkable animals – including ancient giant tortoises, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been free of frogs and toads.

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

DNA studies indicate that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong foothold on two islands: multiple locations.

The numbers is growing so rapidly that scientists have been finding it difficult to monitor, calculating numbers in the hundreds of thousands on every 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 week and a half, she could locate only a single tagged frog occasionally, suggesting their populations were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says San José. "I'm quite certain 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 really incredible," comments San José.

For the scientists, their nightly vocalizations are useful in estimating their existence in far-flung areas, using recorders like the one outside San José's office.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

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

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

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly 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 common for invasive species to thrive, as they have none of their enemies. The islands has over sixteen hundred introduced types, many of which are significantly disrupting the survival of its endemic ones.

A 2020 study indicates the invasive frogs are voracious bug eaters, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or reducing the food sources of the region's uncommon avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some unusual traits, including surviving in slightly salty water, which is rare for frogs.

Their metamorphosis stage is also highly variable, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which remained as a larva in her laboratory for six months.

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

Methods to curb the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried capturing large numbers by hand and slowly increasing the salinity of ponds in vain.

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

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

Funding Challenges for Research

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

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