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During her daily walk to the scientific station, scientist the researcher crouches near a small water body covered by thick plants and collects a small plastic audio device.

The device was left there overnight to record the distinctive croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with effects that scientists are starting to understand.

Although teeming with unique wildlife – including ancient giant tortoises, marine iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this changed. Some tiny amphibians traveled from continental the mainland to the archipelago, likely as stowaways on transport vessels.

DNA research indicate that, over the years, there have been repeated unintentional arrivals to the archipelago, and the frogs now have a strong foothold on several islands: multiple locations.

The numbers is expanding so rapidly that researchers have been finding it difficult to monitor, estimating numbers in the millions on each island, across developed and agricultural areas, but also in the protected natural reserve.

When the biologist marked frogs and attempted to recapture them in the following 10 days, she could locate only a single tagged frog occasionally, suggesting their populations were enormous.

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," states the researcher. "I'm pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the acoustic chaos they create. "The number of frogs and the sound – it's really insane," says San José.

For the researchers, their nightly mating calls are useful in determining their existence in remote areas, using audio devices like the one outside San José's workplace.

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

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

"Initially it was a surprise, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about several years ago when one leaped on her palm as she was walking out of her house.

Ecological Impact Stays Unclear

The sound isn't the primary problem, however. While the amphibians has been in the Galápagos for almost 30 years, experts still know very little about its effect on the archipelago's delicately balanced land and water environments.

On archipelagos, it is very common for non-native species to thrive, as they have none of their natural predators. The islands counts over sixteen hundred introduced species, many of which are significantly disrupting the safety of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry bug consumers, and might be disproportionately consuming rare insects found only on the islands, or depleting the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos frogs have exhibited some unusual traits, including living in brackish water, which is rare for frogs.

Their metamorphosis stage is also highly inconsistent, with some tadpoles turning into frogs very quickly and others taking a extended period: the researcher witnessed one which stayed as a larva in her laboratory for six months.

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

Techniques to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting large numbers by manual methods and gradually increasing the salinity of ponds in without success.

Research indicates applying caffeine – which is extremely poisonous to amphibians – or using electrocution could assist, but these approaches aren't always secure for other uncommon island organisms.

Lacking solutions to more of the fundamental questions about their lifestyle and effect, culling the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she hopes the increasing use of environmental DNA techniques and genetic analysis will assist her group make sense of the invasive species, funding for the project has been hard to come by.

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