Galápagos Had No Indigenous Amphibians. Until Hundreds of Thousands of Frogs Made Their Home

During her daily commute to the scientific station, biologist the researcher stoops near a shallow water body surrounded by thick vegetation and collects a small green sound recorder.

The device was left there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, known by Galápagos researchers as an non-native species with effects that scientists are just beginning to understand.

Despite teeming with unique animals – including ancient giant tortoises, marine iguanas, and the famous birds that sparked Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some tiny amphibians made their way from mainland the mainland to the archipelago, likely as hitchhikers on transport vessels.

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

The population is growing so rapidly that researchers have been finding it difficult to keep track, estimating populations in the millions on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to find them in the following 10 days, she could locate just one tagged frog from time to time, suggesting their numbers were enormous.

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," says the researcher. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

The amphibians' proliferation is clear from the acoustic disruption they cause. "The amount of frogs and the noise – it's truly insane," comments the scientist.

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

But local farmers say the sounds are so loud they keep them up at night.

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

"Initially it was a surprise, seeing the first frogs in the region," says Larrea Saltos, who started observing their large numbers about several years ago when one leaped on her palm as she was walking out of her house.

Environmental Consequences Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, experts still know very little about its effect on the islands' precariously balanced land and water ecosystems.

On islands, it is very common for invasive species to thrive, as they have none of their natural predators. The Galápagos has 1,645 introduced species, many of which are significantly affecting the survival of its endemic ones.

A recent research suggests the invasive frogs are voracious insect eaters, and might be disproportionately eating uncommon bugs found exclusively on the archipelago, or depleting the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos amphibians have exhibited some atypical characteristics, including living in brackish water, which is uncommon for frogs.

Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a long time: the researcher observed one which stayed as a larva in her lab for half a year.

"We really don't know this part," she says, concerned the larvae could be impacting the region's freshwater, a very limited resource in Galápagos.

Techniques to control the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried collecting significant quantities by hand and slowly raising the salinity of lagoons in vain.

Research indicates applying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon island species.

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

Funding Challenges for Study

While she expects the growing use of eDNA methods and DNA examination will assist her group understand of the invasive species, financial support for the project has been hard to come by.

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