On her daily commute to the scientific station, scientist the researcher crouches near a shallow pond surrounded by thick plants and collects a small plastic sound device.
She had placed there through the night to record the distinctive croaks of the Scinax quinquefasciatus, known by local researchers as an non-native species with consequences that scientists are starting to comprehend.
Despite abounding with remarkable animals – including ancient giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's evolutionary theory – the island chain near the shoreline of South America had historically been devoid of frogs and toads.
In the late 1990s, this shifted. Some tiny tree frogs made their way from mainland the mainland to the archipelago, likely as stowaways on cargo ships.
Genetic studies indicate that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong presence on two locations: Isabela and Santa Cruz.
The numbers is expanding so quickly that scientists have been struggling to keep track, calculating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the conservation natural reserve.
When the biologist tagged amphibians and attempted to recapture them in the following 10 days, she could find just one marked frog from time to time, indicating their numbers were enormous.
They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are additional numbers."
Deafening Noise and Rising Worries
The frogs' abundance is clear from the acoustic chaos they create. "The number of frogs and the noise – it's truly incredible," says San José.
For the researchers, their nightly mating calls are helpful in determining their presence in far-flung areas, using audio devices like the one outside the office.
But local agricultural workers say the sounds are so raucous they keep them up at night.
"During the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.
"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started noticing their abundance about several years ago when one jumped on her hand as she was walking out of her front door.
Ecological Impact Remains Unknown
The sound isn't the primary problem, though. While the amphibians has been in the islands for almost three decades, scientists still know limited information about its effect on the archipelago's delicately balanced land and water environments.
On archipelagos, it is very common for non-native species to prosper, as they have none of their natural predators. The Galápagos has over sixteen hundred introduced species, many of which are significantly affecting the survival of its endemic ones.
A 2020 research indicates the invasive amphibians are voracious bug eaters, and might be unevenly eating rare insects found only on the archipelago, or reducing the food sources of the region's uncommon birds, disrupting the ecosystem balance.
Unusual Traits and Management Difficulties
The Galápagos amphibians have exhibited some unusual traits, including surviving in brackish water, which is uncommon for frogs.
Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a long time: San José witnessed one which remained as a tadpole in her lab for half a year.
"We truly don't know this part," she says, worried the larvae could be affecting the islands' freshwater, a very limited commodity in the islands.
Methods to curb the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by hand and gradually increasing the salinity of ponds in without success.
Research suggests applying caffeine – which is extremely toxic to frogs – or using electrocution could assist, but these methods aren't necessarily safe for other rare Galápagos species.
Without answers to more of the basic issues about their lifestyle and impact, removing the frogs might not even be the right way to advance, says San José.
Financial Obstacles for Study
While she hopes the growing use of eDNA techniques and genetic analysis will help her group understand of the invader, financial support for the project has been hard to come by.
"Everyone wants to give funding for protecting frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to manage."
