🔗 Share this article

During her daily walk to the research facility, scientist Miriam San José stoops near a shallow water body covered by dense vegetation and collects a compact plastic sound recorder.

She had placed there overnight to record the distinctive croaks of the Fowler's snouted treefrog, known by Galápagos researchers as an non-native species with consequences that scientists are just beginning to comprehend.

Despite abounding with remarkable wildlife – including centuries-old large turtles, marine iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been free of amphibians.

During the 1990s, this shifted. Several small amphibians made their way from mainland Ecuador to the archipelago, likely as stowaways on transport vessels.

Genetic studies suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the frogs now have a firm presence on several locations: Isabela and Santa Cruz.

The numbers is growing so rapidly that researchers have been struggling to keep track, estimating numbers in the millions on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to recapture them in the following week and a half, she could find only a single marked frog from time to time, suggesting their populations were massive.

They estimated 6,000 frogs in a single pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are even more."

Deafening Noise and Growing Concerns

The frogs' proliferation is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's truly incredible," says San José.

For the scientists, their nocturnal mating calls are useful in estimating their presence in remote areas, using audio devices like the one near the office.

But nearby agricultural workers say the calls are so raucous they prevent sleep at night.

"During the rainy period, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

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

Environmental Consequences Stays Unclear

The sound isn't the fundamental problem, however. While the amphibians has been in the islands for nearly three decades, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native species to prosper, as they have few of their natural predators. The islands has over sixteen hundred invasive species, many of which are significantly affecting the survival of its native ones.

A 2020 study suggests the invasive frogs are voracious bug eaters, and might be disproportionately consuming rare bugs found only on the islands, or depleting the food sources of the region's uncommon birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their development stage is also highly inconsistent, with some larvae becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for half a year.

"We truly don't know this aspect," she says, concerned the tadpoles could be affecting the islands' clean water, a very scarce commodity in Galápagos.

Methods to control the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried collecting significant quantities by hand and gradually increasing the salt content of ponds in vain.

Studies indicates applying coffee – which is extremely poisonous to amphibians – or using electrocution could help, but these approaches aren't always safe for other uncommon island species.

Without solutions to more of the fundamental questions about their biology and impact, culling the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Research

While she expects the increasing use of eDNA techniques and genetic examination will help her team understand of the invader, financial support for the project has been difficult to obtain.

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