🔗 Share this article

During her regular walk to the scientific station, scientist the researcher stoops near a small pond surrounded by thick vegetation and collects a small green audio device.

She had placed there overnight to capture the characteristic croaks of the Fowler's snouted treefrog, known by local researchers as an non-native threat with consequences that experts are just beginning to understand.

Although teeming with unique animals – such as centuries-old giant tortoises, marine lizards, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had long remained devoid of amphibians.

In the late 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

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

The numbers is growing so quickly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the protected Galápagos national park.

When the biologist tagged frogs and attempted to find them in the subsequent week and a half, she could locate just one tagged frog from time to time, indicating their populations were massive.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," states San José. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's really insane," says San José.

For the researchers, their nocturnal mating calls are useful in determining their presence in remote areas, using recorders like the one outside San José's workplace.

But local farmers say the sounds are so raucous they prevent sleep at night.

"In the wet season, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

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

Environmental Consequences Remains Unclear

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

On archipelagos, it is very common for non-native species to prosper, as they have none of their enemies. The islands counts 1,645 introduced types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study suggests the non-native amphibians are hungry bug eaters, and might be disproportionately consuming rare bugs found only on the islands, or depleting the food sources of the region's rare avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have exhibited some unusual characteristics, including living in brackish water, which is rare for frogs.

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

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

Methods to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by hand and gradually increasing the salinity of ponds in vain.

Studies indicates spraying coffee – which is highly poisonous to frogs – or using electrocution could assist, but these approaches aren't necessarily secure for other uncommon island species.

Without answers to more of the basic questions about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA techniques and genetic examination will assist her group understand of the invasive species, financial support for the research has been hard to obtain.

"Everyone wants to give support for preserving frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to manage."