🔗 Share this article

During her regular commute to the scientific station, scientist the researcher stoops near a small pond surrounded by dense vegetation and collects a compact green sound device.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by local scientists as an invasive species with consequences that scientists are just beginning to comprehend.

Although teeming with unique wildlife – including centuries-old giant tortoises, swimming lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Some tiny tree frogs made their way from continental Ecuador to the archipelago, probably as hitchhikers on transport vessels.

Genetic research suggest that, through time, there have been repeated accidental introductions to the islands, 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 populations in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could find only a single tagged frog from time to time, indicating their populations were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is evident from the sound chaos they cause. "The amount of frogs and the noise – it's really insane," says San José.

For the researchers, their nightly mating calls are helpful in determining their presence in remote areas, using recorders like the one near San José's workplace.

But nearby agricultural workers say the sounds are so raucous they keep them up at night.

"In the wet season, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, observing the first frogs in the area," says the farmer, who started observing their large numbers about three years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Stays Unclear

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

On archipelagos, it is very common for non-native species to prosper, as they have none of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are significantly disrupting the survival of its native ones.

A 2020 study indicates the non-native amphibians are voracious insect eaters, and might be unevenly consuming uncommon insects found only on the islands, or depleting the food sources of the islands' uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their development process is also extremely inconsistent, with some larvae becoming frogs very rapidly and others taking a long time: San José observed one which stayed as a larva in her lab for half a year.

"We truly don't know this part," she says, worried the larvae could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried collecting significant quantities by manual methods and gradually increasing the salinity of ponds in without success.

Research indicates applying coffee – which is highly poisonous to amphibians – or using electrocution could help, but these approaches aren't necessarily safe for other rare island organisms.

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

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and DNA analysis will help her team understand of the invasive species, financial support for the project has been hard to obtain.

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