🔗 Share this article

On her daily commute to the scientific station, biologist the researcher crouches near a small water body covered by thick plants and collects a small green sound recorder.

She had placed there overnight to record the distinctive calls of the Scinax quinquefasciatus, known by local scientists as an invasive species with effects that experts are just beginning to comprehend.

Despite abounding with remarkable animals – such as centuries-old giant tortoises, swimming iguanas, and the famous birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as hitchhikers on transport vessels.

Genetic research suggest that, over the years, there have been repeated accidental arrivals to the archipelago, and the frogs now have a firm foothold on two islands: multiple locations.

The numbers is growing so quickly that researchers have been struggling to keep track, estimating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the protected natural reserve.

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

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," states San José. "I am quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the sound chaos they cause. "The number of frogs and the sound – it's truly insane," comments the scientist.

For the scientists, their nightly vocalizations are useful in determining their existence in remote areas, using recorders like the one outside the workplace.

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

"In the rainy period, I regularly hear their croaks and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, observing the first 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 front door.

Ecological Impact Remains Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost three decades, experts still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for non-native species to thrive, as they have none of their enemies. The Galápagos has 1,645 invasive types, many of which are significantly affecting the survival of its endemic ones.

A 2020 study suggests the non-native frogs are hungry bug consumers, and might be disproportionately consuming rare bugs found only on the archipelago, or reducing the food sources of the islands' rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have exhibited some unusual characteristics, including living in slightly salty water, which is rare for frogs.

Their development stage is also highly inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher witnessed one which stayed as a tadpole in her lab for six months.

"We really don't know this part," she says, concerned the tadpoles could be affecting the region's clean water, a very limited resource in the islands.

Techniques to control the amphibians in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by hand and gradually raising the salt content of lagoons in without success.

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

Without solutions to more of the basic questions about their lifestyle and effect, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of eDNA techniques and DNA analysis will assist her group understand of the invasive species, funding for the project has been hard to obtain.

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