During her regular walk to the scientific station, biologist Miriam San José stoops near a shallow pond covered by thick plants and retrieves a small green audio recorder.
The device was left there through the night to record the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with effects that experts are just beginning to comprehend.
Despite abounding with unique animals – including centuries-old large turtles, marine iguanas, and the famous finches that inspired Darwin's theory of evolution – the island chain off the coast of South America had long remained free of frogs and toads.
In the late 1990s, this changed. Some small amphibians traveled from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.
DNA studies suggest that, over the years, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm foothold on two islands: multiple locations.
The numbers is expanding so rapidly that scientists have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across developed and agricultural areas, but also in the conservation Galápagos national park.
When the biologist marked amphibians and attempted to recapture them in the following 10 days, she could locate just one tagged frog from time to time, indicating their populations were enormous.
They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," states the researcher. "I'm pretty sure there are even more."
Deafening Noise and Rising Worries
The frogs' proliferation is evident from the acoustic disruption they cause. "The number of frogs and the noise – it's truly incredible," comments San José.
For the researchers, their nocturnal mating calls are useful in estimating their presence in remote areas, using recorders like the one near San José's workplace.
But local agricultural workers say the sounds are so loud they prevent sleep at night.
"During the wet season, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.
"At first it was a surprise, observing the first frogs in the area," says the farmer, who started noticing their large numbers about three years ago when one jumped on her palm as she was walking out of her front door.
Environmental Consequences Remains Unknown
The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, experts still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.
On archipelagos, it is very typical for invasive organisms to thrive, as they have none of their enemies. The islands has 1,645 invasive types, many of which are significantly disrupting the survival of its endemic ones.
A recent study indicates the non-native amphibians are voracious insect consumers, and might be unevenly consuming rare bugs found exclusively on the archipelago, or reducing the nutrition of the islands' uncommon birds, affecting the ecosystem balance.
Unique Characteristics and Control Challenges
The island frogs have shown some unusual traits, including living in slightly salty water, which is rare for amphibians.
Their development stage is also highly inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: San José observed one which stayed as a tadpole in her laboratory for six months.
"We really don't know this part," she says, concerned the tadpoles could be impacting the region's clean water, a very scarce commodity in Galápagos.
Methods to curb the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried collecting significant quantities by hand and gradually increasing the salinity of lagoons in without success.
Research suggests applying caffeine – which is highly toxic to amphibians – or using electrical methods could help, but these methods aren't always safe for other uncommon Galápagos organisms.
Lacking solutions to more of the basic questions about their biology and impact, removing the amphibians might not even be the right way to advance, says the biologist.
Financial Obstacles for Study
While she hopes the growing use of eDNA methods and DNA analysis will help her group understand of the invasive species, financial support for the project has been hard to come by.
"Everyone wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to manage."
