🔗 Share this article

During her daily commute to the research facility, biologist Miriam San José crouches near a shallow pond surrounded by thick plants and collects a compact green audio recorder.

The device was left there overnight to capture the characteristic croaks of the Fowler's snouted treefrog, known by local scientists as an invasive threat with effects that scientists are starting to comprehend.

Despite abounding with unique wildlife – such as ancient large turtles, swimming lizards, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had long remained free of amphibians.

During the 1990s, this shifted. Some tiny amphibians traveled from continental the mainland to the archipelago, probably as hitchhikers on transport vessels.

DNA research suggest that, over the years, there have been multiple accidental introductions to the archipelago, and the frogs now have a firm presence on two locations: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to keep track, calculating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the protected 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 tagged frog occasionally, indicating their populations were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is clear from the sound chaos they create. "The amount of frogs and the noise – it's really incredible," comments the scientist.

For the researchers, their nocturnal mating calls are helpful in estimating their existence in far-flung areas, using audio devices like the one outside the workplace.

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

"In the wet season, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a surprise, observing the first frogs in the region," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, however. While the species has been in the Galápagos for almost three decades, scientists still know limited information about its effect on the islands' precariously balanced land and water environments.

On islands, it is very common for invasive organisms to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 research suggests the non-native frogs are hungry bug consumers, and might be unevenly eating rare insects found only on the islands, or depleting the food sources of the islands' rare avian species, affecting the food chain.

Unique Characteristics and Control Challenges

The island frogs have shown some atypical traits, including surviving in brackish water, which is rare for amphibians.

Their metamorphosis process is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a larva in her laboratory for six months.

"We truly don't know this aspect," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited resource in Galápagos.

Techniques to control the amphibians in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by hand and slowly raising the salinity of lagoons in vain.

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

Lacking solutions to more of the basic questions about their biology and impact, removing the frogs might not even be the correct way to proceed, says the biologist.

Funding Challenges for Study

While she expects the increasing use of eDNA methods and DNA examination will assist her team make sense of the invader, financial support for the research has been hard to obtain.

"Everybody wants to give support for protecting frogs," says San José. "But it's more difficult to find funding for an introduced frog that you might want to manage."