🔗 Share this article

During her daily walk to the research facility, scientist the researcher stoops near a small water body covered by dense plants and retrieves a compact green sound recorder.

The device was left there through the night to record the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native species with effects that experts are starting to comprehend.

Despite teeming with remarkable wildlife – including ancient large turtles, marine iguanas, and the famous finches that inspired Charles Darwin's theory of evolution – the island chain off the coast of South America had long remained devoid of frogs and toads.

In the late 1990s, this changed. Some small tree frogs traveled from mainland Ecuador to the archipelago, probably as stowaways on cargo ships.

Genetic research suggest that, over the years, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm foothold on two locations: multiple locations.

The population is growing so quickly that scientists have been struggling to keep track, calculating numbers in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When San José tagged amphibians and attempted to find them in the subsequent week and a half, she could find only a single 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 conservative," states the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' abundance is clear from the sound disruption they cause. "The number of frogs and the noise – it's really incredible," says San José.

For the scientists, their nocturnal mating calls are helpful in determining their presence in remote areas, using audio devices like the one near the office.

But local farmers say the calls are so loud they prevent sleep at night.

"In the rainy period, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know limited information about its impact on the archipelago's delicately balanced land and water environments.

On archipelagos, it is very common for invasive species to prosper, as they have few of their enemies. The Galápagos counts 1,645 introduced species, many of which are seriously disrupting the safety of its endemic ones.

A 2020 study suggests the invasive frogs are voracious insect consumers, and might be disproportionately consuming uncommon insects found only on the islands, or depleting the nutrition of the islands' uncommon birds, affecting the food chain.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some unusual characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also extremely variable, 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 truly don't know this part," she says, worried the larvae could be impacting the region's freshwater, a very limited commodity in the islands.

Methods to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and gradually increasing the salt content of ponds in without success.

Studies indicates applying caffeine – which is highly toxic to amphibians – or using electrical methods could assist, but these approaches aren't always secure for other rare island species.

Lacking solutions to more of the basic issues about their lifestyle and impact, removing the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the increasing use of eDNA methods and genetic examination will help her group make sense of the invader, funding for the research has been difficult to obtain.

"Everybody wants to give funding for protecting frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to control."