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On her daily walk to the scientific station, biologist Miriam San José crouches near a small pond covered by dense plants and collects a small green sound device.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by local scientists as an invasive threat with consequences that experts are just beginning to understand.

Although abounding with remarkable animals – such as centuries-old giant tortoises, marine lizards, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Several small tree frogs traveled from continental Ecuador to the islands, probably as stowaways on transport vessels.

DNA studies suggest that, over the years, there have been repeated accidental introductions to the islands, and the frogs now have a strong foothold on several locations: Isabela and Santa Cruz.

The numbers is expanding so quickly that researchers have been finding it difficult to monitor, estimating populations in the millions on each island, across developed and farming areas, but also in the protected Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the subsequent 10 days, she could find only a single marked frog occasionally, indicating their numbers were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is clear from the sound chaos they cause. "The number of frogs and the noise – it's really insane," says the scientist.

For the researchers, their nocturnal vocalizations are helpful in determining their existence in far-flung areas, using audio devices like the one outside the workplace.

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

"In the rainy period, 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 region," says the farmer, who started observing their large numbers about several years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly 30 years, scientists still know limited information about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive species to thrive, as they have few of their enemies. The islands counts over sixteen hundred introduced species, many of which are significantly affecting the safety of its native ones.

A 2020 research suggests the invasive amphibians are voracious insect consumers, and might be disproportionately eating uncommon bugs found exclusively on the archipelago, or depleting the nutrition of the islands' uncommon birds, affecting the food chain.

Unique Characteristics and Control Challenges

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

Their development process is also extremely inconsistent, with some tadpoles turning into frogs very quickly and others taking a extended period: San José witnessed one which remained as a tadpole in her lab for six months.

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

Techniques to control the frogs in the beginning of the century were largely ineffective. Conservation officers tried capturing large numbers by hand and slowly raising the salinity of ponds in without success.

Research indicates applying coffee – which is highly toxic to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon island species.

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

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and DNA analysis will help her team make sense of the invader, financial support for the research has been hard to come by.

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