🔗 Share this article

During her regular walk to the scientific station, scientist the researcher crouches near a small pond surrounded by dense vegetation and retrieves a small green audio recorder.

The device was left there through the night to record the characteristic calls of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that scientists are just beginning to comprehend.

Although abounding with unique animals – such as centuries-old large turtles, marine iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the island chain near the coast of South America had long remained free of amphibians.

In the late 1990s, this shifted. Several tiny tree frogs made their way from mainland Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic research indicate that, over the years, there have been repeated unintentional arrivals to the archipelago, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the following week and a half, she could locate just one tagged frog from time to time, suggesting their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," states the researcher. "I'm quite certain there are even more."

Deafening Noise and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they create. "The number of frogs and the noise – it's truly incredible," says San José.

For the researchers, their nocturnal vocalizations are helpful in estimating their existence in far-flung areas, using recorders like the one near the office.

But local agricultural workers say the calls are so loud they prevent sleep at night.

"In the rainy period, 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 initial frogs in the area," says the farmer, who started observing their abundance about several years ago when one leaped on her palm as she was walking out of her front door.

Ecological Impact Stays Unclear

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

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

A 2020 research indicates the non-native frogs are voracious bug consumers, and might be disproportionately consuming uncommon bugs found only on the archipelago, or depleting the food sources of the islands' uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: the researcher witnessed one which stayed as a larva in her lab for half a year.

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

Methods to control the frogs in the early 2000s were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly raising the salt content of lagoons in without success.

Research indicates applying caffeine – which is highly poisonous to frogs – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos species.

Without answers to more of the basic questions about their lifestyle and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she hopes the growing use of environmental DNA methods and genetic examination will assist her group understand of the invasive species, financial support for the research has been difficult to come by.

"Everyone wants to give funding for protecting frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to manage."