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

On her daily walk to the scientific station, biologist the researcher stoops near a small water body surrounded by dense vegetation and collects a small green audio recorder.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with effects that scientists are starting to comprehend.

Despite teeming with remarkable animals – such as ancient large turtles, marine lizards, and the well-known finches that sparked Charles Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this changed. Several small amphibians made their way from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic studies suggest that, through time, there have been repeated accidental arrivals to the archipelago, and the frogs now have a strong presence on two locations: multiple locations.

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

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

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the sound disruption they cause. "The number of frogs and the noise – it's really incredible," comments the scientist.

For the scientists, their nocturnal mating calls are helpful in estimating their existence in remote areas, using recorders like the one near San José's workplace.

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

"During the rainy period, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Stays Unknown

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know limited information about its effect on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very common for invasive species to prosper, as they have none of their natural predators. The Galápagos counts 1,645 introduced species, many of which are significantly disrupting the safety of its native ones.

A recent study indicates the non-native amphibians are hungry insect eaters, and might be disproportionately consuming rare insects found exclusively on the archipelago, or reducing the food sources of the islands' rare birds, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development process is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher observed one which remained as a larva in her lab for six months.

"We truly don't know this aspect," she says, worried the tadpoles could be affecting the islands' freshwater, a very limited resource in Galápagos.

Techniques to control the frogs in the beginning of the century were largely ineffective. Park rangers tried collecting large numbers by manual methods and gradually increasing the salinity of lagoons in without success.

Research suggests spraying caffeine – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't always safe for other uncommon island species.

Without solutions to more of the fundamental issues about their lifestyle and effect, culling the amphibians might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she hopes the increasing use of eDNA methods and DNA analysis will help her group make sense of the invader, funding for the project has been difficult to come by.

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