🔗 Share this article

On her regular walk to the research facility, scientist the researcher crouches near a small water body surrounded by dense plants and retrieves a compact green sound device.

The device was left there overnight to record the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an non-native threat with effects that experts are just beginning to comprehend.

Despite abounding with remarkable wildlife – including centuries-old giant tortoises, marine lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained free of frogs and toads.

In the late 1990s, this shifted. Some small tree frogs made their way from mainland Ecuador to the islands, probably as stowaways on cargo ships.

DNA studies suggest that, through time, there have been multiple unintentional introductions to the archipelago, and the frogs now have a strong foothold on two islands: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been finding it difficult to keep track, estimating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected natural reserve.

When the biologist tagged amphibians and attempted to find them in the subsequent week and a half, she could locate only a single marked frog occasionally, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," says the researcher. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the acoustic disruption they cause. "The amount of frogs and the noise – it's really insane," comments San José.

For the researchers, their nocturnal mating calls are useful in determining their existence in far-flung areas, using audio devices like the one near the office.

But local farmers 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.

"At first it was a shock, observing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one jumped on her hand as she was stepping out of her front door.

Ecological Impact Stays Unclear

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for nearly 30 years, scientists still know very little about its effect on the islands' precariously balanced land and water environments.

On archipelagos, it is very common for non-native organisms to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are significantly disrupting the safety of its native ones.

A recent study indicates the invasive amphibians are hungry insect consumers, and might be unevenly eating rare bugs found exclusively on the islands, or reducing the food sources of the islands' uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

The island amphibians have shown some unusual characteristics, including surviving in brackish water, which is rare for amphibians.

Their metamorphosis process is also highly inconsistent, with some tadpoles turning into frogs very quickly and others taking a long time: the researcher witnessed one which remained as a tadpole in her laboratory for half a year.

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

Techniques to curb the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried collecting large numbers by manual methods and slowly raising the salt content of ponds in without success.

Research indicates spraying caffeine – which is extremely poisonous to amphibians – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos organisms.

Lacking answers to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she expects the growing use of eDNA methods and DNA analysis will help her team make sense of the invader, funding for the project has been difficult to obtain.

"Everyone wants to give funding for protecting frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to control."