🔗 Share this article

On her daily commute to the research facility, biologist Miriam San José crouches near a small water body covered by dense vegetation and collects a compact plastic audio recorder.

She had placed 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 experts are starting to comprehend.

Although abounding with unique wildlife – such as centuries-old giant tortoises, marine lizards, and the famous birds that inspired Darwin's theory of evolution – the island chain near the shoreline of South America had historically been free of frogs and toads.

In the late 1990s, this shifted. Several small amphibians made their way from mainland the mainland to the islands, likely as stowaways on transport vessels.

Genetic research suggest that, through time, there have been repeated unintentional arrivals to the archipelago, and the amphibians now have a firm foothold on several islands: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been struggling to keep track, calculating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the conservation Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the subsequent week and a half, she could find just one tagged frog from time to time, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' abundance is evident from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," comments the scientist.

For the scientists, their nightly mating calls are helpful in determining their presence in far-flung areas, using audio devices like the one outside the workplace.

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

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

"At first it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unclear

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know limited information about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very common for non-native organisms to prosper, as they have few of their natural predators. The islands has 1,645 invasive species, many of which are significantly affecting the survival of its native ones.

A recent study suggests the invasive amphibians are voracious bug consumers, and might be disproportionately consuming rare bugs found only on the archipelago, or depleting the nutrition of the islands' rare birds, affecting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some atypical characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their development process is also highly variable, with some larvae turning into frogs very rapidly 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 aspect," she says, worried the larvae could be impacting the region's clean water, a very limited commodity in the islands.

Techniques to control the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried collecting significant quantities by manual methods and gradually raising the salinity of ponds in vain.

Studies indicates applying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon island species.

Lacking solutions to more of the basic questions about their biology and effect, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of environmental DNA methods and genetic examination will help her group make sense of the invader, funding for the research has been hard to come by.

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