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During her daily commute to the scientific station, scientist Miriam San José stoops near a small pond surrounded by dense vegetation and collects a compact plastic sound recorder.

She had placed there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with effects that experts are just beginning to understand.

Although teeming with unique animals – such as centuries-old large turtles, marine lizards, and the well-known finches that inspired Darwin's theory of evolution – the island chain near the shoreline of South America had long remained free of frogs and toads.

During the 1990s, this shifted. Several small tree frogs traveled from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

Genetic studies suggest that, through time, there have been repeated unintentional introductions to the archipelago, and the frogs now have a firm presence on two locations: Isabela and Santa Cruz.

The population is growing so rapidly that researchers have been struggling to keep track, estimating populations in the millions on each island, across urban and farming areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to find them in the subsequent 10 days, she could find only a single tagged frog from time to time, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "Our estimates are still very low," states San José. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' proliferation is clear from the acoustic chaos they cause. "The number of frogs and the noise – it's truly incredible," says the scientist.

For the researchers, their nocturnal vocalizations are helpful in determining their presence in remote areas, using audio devices like the one near the office.

But nearby agricultural workers say the calls are so loud they keep them up at night.

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

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

Ecological Impact Remains Unknown

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

On archipelagos, it is very common for invasive organisms to thrive, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced types, many of which are seriously disrupting the safety of its endemic ones.

A 2020 research suggests the non-native amphibians are hungry bug eaters, and might be unevenly eating uncommon bugs found exclusively on the islands, or depleting the nutrition of the islands' rare birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The island amphibians have exhibited some unusual characteristics, including surviving in slightly salty water, which is uncommon for amphibians.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a long time: San José observed one which stayed as a larva in her lab for six months.

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

Methods to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually raising the salinity of lagoons in vain.

Studies suggests spraying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these approaches aren't necessarily secure for other uncommon island organisms.

Without solutions to more of the fundamental questions about their lifestyle and impact, removing the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and genetic analysis will assist her group make sense of the invasive species, funding 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 introduced frog that you might want to manage."