🔗 Share this article

On her regular commute to the scientific station, scientist Miriam San José crouches near a small water body covered by dense plants and retrieves a small green 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 consequences that experts are just beginning to comprehend.

Although abounding with unique wildlife – including ancient giant tortoises, marine lizards, and the well-known finches that sparked Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had historically been devoid of frogs and toads.

During the 1990s, this changed. Several small amphibians made their way from continental Ecuador to the islands, probably as hitchhikers on transport vessels.

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

The population is expanding so rapidly that researchers have been struggling to keep track, calculating numbers in the millions on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to find them in the subsequent week and a half, she could locate just one marked frog from time to time, indicating their populations were enormous.

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

Deafening Noise and Rising Worries

The amphibians' proliferation is evident from the acoustic disruption they create. "The amount of frogs and the sound – it's really insane," says San José.

For the scientists, their nightly mating calls are useful in estimating their existence in remote areas, using recorders like the one near San José's workplace.

But nearby agricultural workers say the sounds are so raucous they prevent sleep at night.

"During the rainy period, I constantly hear their croaks and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, observing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about three years ago when one jumped on her palm as she was walking out of her front door.

Environmental Consequences Remains Unclear

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for almost 30 years, experts still know limited information about its effect on the islands' precariously balanced land and water environments.

On archipelagos, it is very common for invasive organisms to prosper, as they have few of their natural predators. The islands has over sixteen hundred invasive species, many of which are significantly disrupting the safety of its native ones.

A 2020 study suggests the non-native frogs are voracious insect consumers, and might be disproportionately eating uncommon bugs found only on the archipelago, or depleting the nutrition of the region's uncommon birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The island frogs have exhibited some unusual characteristics, including living in brackish water, which is uncommon for frogs.

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

"We really don't know this aspect," she says, concerned the larvae could be impacting the islands' freshwater, a very limited commodity in Galápagos.

Techniques to control the frogs in the early 2000s were largely unsuccessful. Conservation officers tried collecting significant quantities by hand and slowly raising the salt content of lagoons in vain.

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

Lacking solutions to more of the basic questions about their lifestyle and effect, culling the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA methods and DNA analysis will assist her team understand of the invasive species, funding for the project has been difficult to obtain.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's harder to find funding for an invasive frog that you might want to manage."