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During her daily walk to the scientific station, biologist Miriam San José stoops near a shallow water body covered by dense plants and retrieves a compact plastic sound device.

The device was left there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive threat with consequences that scientists are starting to understand.

Although teeming with unique animals – such as centuries-old large turtles, marine lizards, and the famous birds that inspired Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs traveled from continental Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic research suggest that, over the years, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm presence on two locations: multiple locations.

The population is growing so quickly that researchers have been struggling to keep track, calculating populations in the millions on every island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José tagged frogs and attempted to recapture them in the subsequent 10 days, she could locate just one tagged frog from time to time, indicating their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states San José. "I'm quite certain there are additional numbers."

Deafening Noise and Growing Concerns

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

For the researchers, their nightly mating calls are helpful in estimating their presence in remote areas, using recorders like the one near the office.

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

"In the wet season, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a shock, observing the first frogs in the region," says the farmer, who started observing their abundance about several years ago when one leaped on her palm as she was walking out of her front door.

Ecological Impact Remains Unknown

The sound isn't the fundamental problem, however. While the species has been in the islands for nearly three decades, scientists still know limited information about its impact on the archipelago's precariously balanced land and water environments.

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

A recent study suggests the invasive frogs are voracious bug consumers, and might be unevenly eating uncommon insects found only on the archipelago, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also highly inconsistent, 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 half a year.

"We really don't know this part," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited commodity in the islands.

Techniques to curb the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried collecting large numbers by hand and gradually raising the salt content of lagoons in vain.

Studies suggests spraying caffeine – which is extremely poisonous to frogs – or using electrocution could help, but these methods aren't always secure for other rare island organisms.

Lacking answers to more of the basic questions about their lifestyle and impact, removing the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she hopes the increasing use of eDNA methods and DNA examination will assist her group make sense of the invader, funding for the project has been difficult to come by.

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