🔗 Share this article

On her regular walk to the scientific station, biologist the researcher crouches near a small pond covered by thick vegetation and retrieves a compact plastic audio device.

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

Despite abounding with remarkable animals – including centuries-old large turtles, marine lizards, and the famous finches that sparked Charles Darwin's theory of evolution – the island chain off the shoreline of South America had historically been devoid of frogs and toads.

During the 1990s, this changed. Some tiny amphibians made their way from mainland the mainland to the archipelago, probably as hitchhikers on cargo ships.

DNA studies indicate that, through time, there have been repeated accidental arrivals to the islands, and the frogs now have a firm presence on two locations: Isabela and Santa Cruz.

The population is expanding so rapidly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation Galápagos national park.

When the biologist marked amphibians and attempted to find them in the following week and a half, she could find only a single tagged frog occasionally, indicating their numbers were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nightly mating calls are helpful in estimating their existence in far-flung areas, using recorders like the one outside the workplace.

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

"During 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 surprise, seeing the initial frogs in the area," says the farmer, who started observing their large numbers about several years ago when one jumped on her palm as she was stepping out of her house.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for almost three decades, scientists still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for invasive species to thrive, as they have few of their natural predators. The islands has over sixteen hundred invasive types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are hungry insect consumers, and might be unevenly eating uncommon insects found only on the islands, or reducing the nutrition of the region's rare avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development stage is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a extended period: the researcher witnessed one which remained as a tadpole in her laboratory for half a year.

"We really don't know this aspect," she says, concerned the larvae could be impacting the region's freshwater, a very scarce resource in the islands.

Techniques to control the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried capturing large numbers by manual methods and slowly increasing the salinity of lagoons in without success.

Research suggests applying coffee – which is highly poisonous to amphibians – or using electrical methods could assist, but these methods aren't necessarily secure for other uncommon Galápagos organisms.

Lacking answers to more of the fundamental questions about their biology and effect, removing the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and genetic examination will assist her group make sense of the invasive species, financial support for the research has been difficult to obtain.

"Everyone 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 control."