🔗 Share this article

During her regular walk to the scientific station, scientist Miriam San José crouches near a small water body covered by thick vegetation and collects a compact green sound device.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, known by local researchers as an non-native threat with effects that experts are just beginning to understand.

Despite teeming with unique wildlife – including centuries-old giant tortoises, marine lizards, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had long remained free of frogs and toads.

In the late 1990s, this changed. Several tiny amphibians made their way from mainland Ecuador to the islands, probably as hitchhikers on transport vessels.

DNA studies suggest that, through time, there have been repeated unintentional arrivals to the archipelago, and the frogs now have a strong presence on two locations: multiple locations.

The population is expanding so quickly that scientists have been finding it difficult to monitor, estimating numbers in the millions on each island, across developed and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged frogs and attempted to find them in the following 10 days, she could locate just one tagged frog from time to time, suggesting their numbers were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," says San José. "I am quite certain there are even more."

Deafening Noise and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they create. "The number of frogs and the sound – it's truly insane," comments the scientist.

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

But nearby agricultural workers say the calls are so raucous they keep them up at night.

"In the rainy period, I constantly hear their croaks and they're really loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Stays Unclear

The sound isn't the primary problem, however. While the amphibians has been in the islands for nearly three decades, experts still know limited information about its impact on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very typical for invasive organisms to thrive, as they have few of their enemies. The islands counts over sixteen hundred introduced types, many of which are seriously disrupting the safety of its endemic ones.

A recent research suggests the invasive amphibians are hungry bug eaters, and might be disproportionately consuming uncommon insects found only on the archipelago, or reducing the food sources of the islands' rare birds, affecting the food chain.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some unusual traits, including living in brackish water, which is rare for amphibians.

Their metamorphosis stage is also highly inconsistent, with some larvae turning into frogs very quickly and others taking a long time: San José witnessed one which stayed as a larva in her laboratory for half a year.

"We really don't know this aspect," she says, concerned the larvae could be affecting the islands' freshwater, a very scarce resource in the islands.

Techniques to control the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting significant quantities by hand and gradually raising the salt content of lagoons in without success.

Research indicates spraying coffee – which is extremely toxic to amphibians – or using electrocution could assist, but these methods aren't necessarily secure for other uncommon island species.

Without answers to more of the basic questions about their biology and impact, removing the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and genetic examination will assist her group make sense of the invader, funding for the research has been difficult to come by.

"Everybody wants to give support for preserving frogs," says San José. "But it's more difficult to find funding for an introduced frog that you might want to manage."