Galápagos Lacked Any Native Amphibians. Then Hundreds of Thousands of Amphibians Made Their Home

During her daily commute to the scientific station, biologist Miriam San José crouches near a small water body covered by thick vegetation and retrieves a small plastic sound device.

She had placed there through the night to record the characteristic calls of the Fowler's snouted treefrog, known by local scientists as an invasive threat with consequences that scientists are just beginning to understand.

Despite abounding with unique wildlife – such as centuries-old giant tortoises, marine iguanas, and the famous finches that inspired Charles Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained free of frogs and toads.

During the 1990s, this shifted. Some small amphibians traveled from mainland Ecuador to the islands, likely as hitchhikers on cargo ships.

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

The population is growing so quickly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on each island, across urban and farming areas, but also in the protected Galápagos national park.

When San José tagged amphibians and attempted to find them in the following week and a half, she could find just one tagged frog occasionally, indicating their numbers were massive.

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

Deafening Noise and Rising Worries

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

For the researchers, their nightly mating calls are useful in estimating their existence in remote areas, using recorders like the one near the workplace.

But local agricultural workers say the calls are so raucous they keep them up at night.

"During the rainy period, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, seeing the first frogs in the area," says the farmer, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for non-native species to prosper, as they have few of their natural predators. The Galápagos counts 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

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

Unique Characteristics and Control Challenges

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

Their development process is also extremely inconsistent, with some larvae becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a tadpole in her lab for half a year.

"We really don't know this aspect," she says, concerned the larvae could be impacting the islands' freshwater, a very scarce commodity in Galápagos.

Methods to curb the frogs in the early 2000s were largely ineffective. Conservation officers tried collecting significant quantities by manual methods and gradually raising the salt content of lagoons in vain.

Studies indicates applying coffee – which is highly poisonous to frogs – or using electrocution could help, but these methods aren't necessarily secure for other rare Galápagos species.

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

Financial Obstacles for Research

While she expects the increasing use of environmental DNA methods and genetic analysis will help her group understand of the invasive species, financial support for the project has been hard to come by.

"Everybody wants to give funding for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an invasive frog that you might want to control."