The Galápagos Islands Lacked Any Indigenous Amphibians. Then Hundreds of Thousands of Amphibians Made Their Home

During her regular walk to the research facility, biologist the researcher stoops near a small water body covered by dense plants and collects a compact green audio recorder.

She had placed there through the night to record the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with consequences that scientists are starting to understand.

Although teeming with remarkable wildlife – including centuries-old giant tortoises, swimming lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the island chain near the coast of South America had historically been devoid of frogs and toads.

In the late 1990s, this changed. Several small tree frogs made their way from continental the mainland to the archipelago, likely as stowaways on transport vessels.

Genetic research suggest that, over the years, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm presence on two islands: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to monitor, calculating populations in the millions on each island, across developed and agricultural areas, but also in the protected natural reserve.

When San José tagged frogs and attempted to find them in the following week and a half, she could locate only a single marked frog occasionally, indicating their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I am pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the sound disruption they create. "The number of frogs and the sound – it's truly insane," comments the scientist.

For the scientists, their nightly mating calls are helpful in estimating their presence in far-flung areas, using recorders like the one near the workplace.

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

"In the rainy period, I constantly hear their calls and they're extremely loud," says a local coffee farmer from the island.

"At first it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started noticing their large numbers about several years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, however. While the species has been in the Galápagos for almost 30 years, experts still know very little about its impact on the islands' precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for non-native species to thrive, as they have none of their natural predators. The Galápagos has 1,645 invasive species, many of which are seriously affecting the safety of its endemic ones.

A recent study indicates the invasive frogs are hungry bug eaters, and might be disproportionately consuming rare insects found only on the islands, or depleting the nutrition of the islands' rare birds, disrupting the food chain.

Unusual Traits and Management Difficulties

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

Their metamorphosis stage is also highly variable, with some larvae becoming 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 really don't know this aspect," she says, worried the tadpoles could be impacting the islands' freshwater, a very limited resource in the islands.

Methods to curb the amphibians in the early 2000s were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually increasing the salt content of lagoons in vain.

Studies suggests applying coffee – which is highly toxic to amphibians – or using electrical methods could help, but these approaches aren't always safe for other rare Galápagos species.

Lacking answers to more of the basic questions about their lifestyle and effect, removing the frogs might not even be the correct way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the increasing use of environmental DNA techniques and DNA analysis will help her team understand of the invasive species, funding for the research has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."