🔗 Share this article

On her regular walk to the research facility, biologist Miriam San José stoops near a small water body covered by thick vegetation and retrieves a compact plastic sound device.

She had placed there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with effects that scientists are just beginning to understand.

Although teeming with remarkable wildlife – such as ancient large turtles, swimming lizards, and the famous finches that sparked Darwin's evolutionary theory – the Galápagos archipelago off the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several tiny tree frogs traveled from mainland the mainland to the archipelago, probably as stowaways on transport vessels.

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

The numbers is expanding so rapidly that scientists have been finding it difficult to monitor, calculating populations in the millions on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to recapture them in the subsequent week and a half, she could find just one tagged frog from time to time, suggesting their populations were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very low," says San José. "I'm pretty sure there are even more."

Deafening Noise and Growing Concerns

The frogs' proliferation is evident from the sound disruption they cause. "The amount of frogs and the sound – it's truly incredible," comments the scientist.

For the researchers, their nocturnal vocalizations are useful in estimating their existence in remote areas, using audio devices like the one outside the workplace.

But local agricultural workers say the sounds are so loud they keep them up at night.

"During the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

"At first it was a surprise, observing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about three years ago when one leaped on her palm as she was walking out of her house.

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly 30 years, experts still know limited information about its effect on the archipelago's delicately balanced terrestrial and aquatic environments.

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

A recent study indicates the non-native frogs are hungry insect eaters, and might be disproportionately eating rare bugs found only on the islands, or depleting the nutrition of the islands' rare avian species, affecting the food chain.

Unusual Traits and Control Challenges

The Galápagos frogs have shown some unusual characteristics, including surviving in slightly salty water, which is uncommon for amphibians.

Their development process is also highly inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a larva in her laboratory for half a year.

"We truly don't know this aspect," she says, worried the tadpoles could be affecting the islands' clean water, a very limited resource in the islands.

Methods to control the amphibians in the early 2000s were mostly ineffective. Conservation officers tried collecting significant quantities by hand and slowly raising the salt content of ponds in without success.

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

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

Financial Obstacles for Study

While she expects the increasing use of eDNA methods and DNA examination will help her group understand of the invader, funding for the research has been hard to obtain.

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