🔗 Share this article

On her daily walk to the scientific station, scientist Miriam San José stoops near a small water body surrounded by thick plants and retrieves a small plastic audio recorder.

The device was left there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive species with effects that experts are starting to comprehend.

Despite teeming with remarkable animals – such as ancient giant tortoises, marine lizards, and the well-known birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained free of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been multiple accidental introductions to the archipelago, and the amphibians now have a firm foothold on two locations: multiple locations.

The numbers is expanding so quickly that scientists have been finding it difficult to keep track, calculating numbers in the millions on every island, across developed and farming areas, but also in the protected natural reserve.

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

They estimated six thousand frogs in a single pond. "The calculations are still very conservative," states the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nightly vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one near San José's office.

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

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

"Initially it was a surprise, observing the first frogs in the area," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Stays Unclear

The sound isn't the primary problem, however. While the species has been in the Galápagos for almost three decades, experts still know limited information about its impact on the archipelago's precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very common for invasive organisms to prosper, as they have none of their enemies. The islands counts 1,645 invasive types, many of which are significantly affecting the safety of its endemic ones.

A 2020 research indicates the invasive frogs are voracious bug eaters, and might be unevenly eating rare bugs found exclusively on the archipelago, or reducing the food sources of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a long time: San José observed one which stayed as a larva in her laboratory for six months.

"We truly don't know this aspect," she says, worried the larvae could be affecting the islands' freshwater, a very scarce resource in the islands.

Techniques to curb the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried collecting large numbers by hand and gradually raising the salinity of ponds in without success.

Research suggests applying coffee – which is highly poisonous to frogs – or using electrical methods could help, but these methods aren't always safe for other rare Galápagos organisms.

Without answers to more of the basic issues about their lifestyle and effect, removing the frogs might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

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

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