🔗 Share this article

On her regular commute to the research facility, scientist the researcher stoops near a shallow water body surrounded by dense plants and collects a compact green sound recorder.

She had placed there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with effects that experts are starting to understand.

Although teeming with remarkable wildlife – such as centuries-old large turtles, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain off the shoreline of South America had long remained devoid of amphibians.

In the late 1990s, this shifted. Several tiny amphibians traveled from continental Ecuador to the islands, probably as stowaways on cargo ships.

DNA studies indicate that, over the years, there have been multiple unintentional introductions to the archipelago, and the frogs now have a strong presence on several locations: multiple locations.

The population is growing so quickly that researchers have been struggling to keep track, estimating populations in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent week and a half, she could locate just one tagged frog occasionally, indicating their numbers were enormous.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's truly insane," comments San José.

For the researchers, their nocturnal vocalizations are helpful in estimating their existence in remote areas, using audio devices like the one outside San José's office.

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

"During the wet season, I regularly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, observing the first frogs in the region," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the amphibians has been in the islands for almost 30 years, scientists still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On islands, it is very typical for invasive organisms to thrive, as they have few of their natural predators. The islands counts over sixteen hundred invasive types, many of which are seriously disrupting the survival of its native ones.

A 2020 research suggests the invasive amphibians are voracious bug consumers, and might be disproportionately consuming uncommon insects found only on the islands, or depleting the nutrition of the islands' uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

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

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

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

Techniques to curb the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried capturing large numbers by hand and gradually increasing the salinity of lagoons in without success.

Studies suggests applying caffeine – which is extremely toxic to frogs – or using electrical methods could assist, but these approaches aren't always safe for other rare Galápagos species.

Lacking answers to more of the fundamental questions about their lifestyle and impact, culling the amphibians might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA methods and genetic examination will assist her team understand of the invasive species, financial support for the research has been hard to come by.

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