🔗 Share this article

On her regular walk to the research facility, biologist Miriam San José crouches near a small pond covered by dense plants and collects a compact plastic sound recorder.

She had placed there overnight to record the distinctive croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native species with effects that scientists are just beginning to comprehend.

Although abounding with remarkable wildlife – including ancient large turtles, swimming iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had long remained free of amphibians.

In the late 1990s, this shifted. Several small amphibians made their way from mainland Ecuador to the islands, probably as stowaways on transport vessels.

Genetic studies suggest that, over the years, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm foothold on several islands: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been struggling to keep track, calculating populations in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When San José tagged frogs and attempted to recapture them in the following 10 days, she could find only a single tagged frog occasionally, indicating their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am pretty sure 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," says San José.

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

But local farmers say the calls are so raucous they prevent sleep at night.

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

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

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly 30 years, experts still know very little about its impact on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very typical for non-native organisms to prosper, as they have few of their enemies. The islands has 1,645 introduced species, many of which are significantly disrupting the survival of its endemic ones.

A recent study suggests the invasive amphibians are hungry bug eaters, and might be unevenly consuming uncommon bugs found exclusively on the islands, or reducing the nutrition of the islands' uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos amphibians have shown some atypical traits, including surviving in brackish water, which is uncommon for frogs.

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

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

Methods to curb the frogs in the beginning of the century were largely ineffective. Park rangers tried collecting large numbers by hand and gradually raising the salinity of ponds in without success.

Studies suggests spraying caffeine – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't always safe for other rare island species.

Without solutions to more of the fundamental issues about their biology and impact, culling the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of eDNA techniques and genetic analysis will help her team understand of the invader, funding for the project has been hard to come by.

"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 control."