On her regular walk to the research facility, scientist Miriam San José stoops near a small water body covered by dense vegetation and collects a small plastic sound recorder.
She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive species with consequences that experts are just beginning to comprehend.
Although teeming with remarkable animals – such as ancient large turtles, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had historically been free of frogs and toads.
In the late 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the archipelago, probably as hitchhikers on transport vessels.
Genetic studies suggest that, over the years, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm foothold on several islands: multiple locations.
The population is growing so rapidly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.
When San José tagged frogs and attempted to recapture them in the subsequent 10 days, she could locate only a single marked frog from time to time, suggesting their populations were enormous.
They calculated six thousand frogs in a single pond. "The calculations are still very low," says the researcher. "I am pretty sure there are even more."
The amphibians' abundance is clear from the sound disruption they cause. "The number of frogs and the noise – it's really incredible," comments San José.
For the researchers, their nocturnal vocalizations are useful in determining their existence in remote areas, using audio devices like the one near the workplace.
But local farmers say the sounds are so raucous they keep them up at night.
"In the rainy period, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.
"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started observing their large numbers about several years ago when one leaped on her hand as she was walking out of her front door.
The noise isn't the primary problem, though. While the species has been in the Galápagos for almost three decades, scientists still know limited information about its effect on the archipelago's delicately balanced terrestrial and aquatic environments.
On islands, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos counts over sixteen hundred invasive types, many of which are significantly affecting the safety of its native ones.
A recent research suggests the non-native amphibians are hungry bug eaters, and might be disproportionately eating rare insects found only on the islands, or depleting the nutrition of the region's uncommon birds, disrupting the ecosystem balance.
The island amphibians have exhibited some atypical traits, including surviving in brackish water, which is uncommon for frogs.
Their metamorphosis process is also highly inconsistent, with some larvae turning into frogs very quickly and others taking a extended period: the researcher observed one which stayed as a tadpole in her lab for half a year.
"We really don't know this aspect," she says, worried the larvae could be affecting the region's clean water, a very limited commodity in the islands.
Methods to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried collecting large numbers by hand and slowly raising the salt content of ponds in vain.
Research indicates spraying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other rare Galápagos organisms.
Without answers to more of the fundamental issues about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says San José.
While she hopes the growing use of environmental DNA techniques and DNA analysis will help her team understand of the invasive species, funding for the project has been hard to obtain.
"Everybody wants to give funding for protecting frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to control."
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