🔗 Share this article

On her regular commute to the research facility, biologist Miriam San José crouches near a shallow pond covered by thick vegetation and collects a small plastic sound recorder.

The device was left there overnight to record the characteristic calls of the Scinax quinquefasciatus, known by local scientists as an invasive species with consequences that experts are just beginning to comprehend.

Despite teeming with remarkable animals – including centuries-old giant tortoises, swimming iguanas, and the well-known birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had historically been devoid of amphibians.

In the late 1990s, this shifted. Some small amphibians traveled from mainland the mainland to the archipelago, likely as hitchhikers on transport vessels.

DNA studies suggest that, through time, there have been multiple accidental arrivals to the archipelago, and the amphibians now have a strong foothold on several islands: multiple locations.

The population is growing so rapidly that scientists have been finding it difficult to monitor, calculating populations in the millions on each island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged amphibians and attempted to find them in the subsequent 10 days, she could locate only a single tagged frog occasionally, indicating their numbers were enormous.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," says San José. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the sound chaos they create. "The number of frogs and the noise – it's really incredible," says the scientist.

For the scientists, their nocturnal mating calls are helpful in determining their existence in remote areas, using audio devices like the one near the workplace.

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

"In the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her palm as she was stepping out of her house.

Ecological Impact Remains Unclear

The sound isn't the primary problem, however. While the species has been in the islands for nearly three decades, scientists still know limited information about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for non-native species to thrive, as they have none of their natural predators. The Galápagos counts over sixteen hundred invasive species, many of which are seriously disrupting the safety of its endemic ones.

A 2020 study indicates the non-native amphibians are voracious insect eaters, and might be disproportionately eating rare bugs found exclusively on the archipelago, or depleting the nutrition of the region's rare avian species, affecting the food chain.

Unusual Traits and Control Challenges

The Galápagos amphibians have exhibited some unusual traits, including surviving in slightly salty water, which is rare for amphibians.

Their development process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her lab for six months.

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

Techniques to control the amphibians in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by manual methods and slowly increasing the salinity of ponds in vain.

Studies suggests applying coffee – which is highly toxic to frogs – or using electrical methods could assist, but these methods aren't necessarily safe for other uncommon Galápagos species.

Without solutions to more of the basic issues about their biology and impact, culling the amphibians might not even be the right way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of environmental DNA methods and DNA analysis will assist her group make sense of the invader, funding for the research has been hard to obtain.

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