During her daily walk to the research facility, scientist Miriam San José stoops near a small water body surrounded by dense vegetation and collects a compact plastic audio recorder.
The device was left there overnight to record the distinctive croaks of the Scinax quinquefasciatus, recognized by local researchers as an non-native threat with effects that scientists are starting to comprehend.
Although abounding with unique animals – such as centuries-old giant tortoises, swimming lizards, and the well-known finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had long remained devoid of amphibians.
During the 1990s, this shifted. Several small tree frogs made their way from continental the mainland to the islands, probably as hitchhikers on transport vessels.
Genetic research indicate that, through time, there have been repeated accidental arrivals to the archipelago, and the amphibians now have a strong foothold on two locations: multiple locations.
The population is growing so rapidly that researchers have been finding it difficult to monitor, calculating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the protected natural reserve.
When San José tagged amphibians and attempted to find them in the following week and a half, she could locate just one marked frog occasionally, suggesting their populations were enormous.
They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are even more."
The amphibians' abundance is clear from the sound chaos they create. "The number of frogs and the sound – it's really insane," comments San José.
For the researchers, their nocturnal mating calls are useful in determining their presence in remote areas, using recorders like the one outside San José's office.
But nearby agricultural workers say the calls are so raucous they prevent sleep at night.
"During the rainy period, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.
"At first it was a shock, seeing the first frogs in the area," says the farmer, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.
The sound isn't the fundamental problem, however. While the species has been in the Galápagos for nearly 30 years, experts still know limited information about its impact on the islands' precariously balanced land and water ecosystems.
On archipelagos, it is very common for non-native organisms to prosper, as they have none of their enemies. The Galápagos has 1,645 introduced types, many of which are significantly affecting the survival of its native ones.
A 2020 study suggests the invasive amphibians are hungry bug consumers, and might be unevenly consuming rare insects found only on the archipelago, or reducing the food sources of the islands' rare birds, affecting the food chain.
The island frogs have exhibited some atypical traits, including surviving in slightly salty water, which is uncommon for amphibians.
Their development process is also highly variable, with some larvae turning into frogs very quickly and others taking a extended period: San José observed one which stayed as a larva in her lab for half a year.
"We truly don't know this aspect," she says, worried the larvae could be affecting the islands' freshwater, a very limited commodity in the islands.
Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting significant quantities by manual methods and slowly increasing the salinity of lagoons in vain.
Studies indicates spraying coffee – which is extremely toxic to frogs – or using electrical methods could help, but these approaches aren't always secure for other rare island organisms.
Lacking answers to more of the basic questions about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says the biologist.
While she expects the increasing use of environmental DNA techniques and genetic examination will help her team understand of the invasive species, financial support for the research has been difficult to come by.
"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to manage."
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