🔗 Share this article

On her regular commute to the scientific station, scientist the researcher stoops near a small water body covered by thick vegetation and retrieves a compact plastic sound recorder.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive species with consequences that scientists are starting to comprehend.

Although abounding with unique animals – such as centuries-old giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's theory of evolution – the Galápagos archipelago near the shoreline of Ecuador had historically been devoid of amphibians.

During the 1990s, this changed. Some tiny tree frogs traveled from mainland the mainland to the islands, likely as stowaways on cargo ships.

Genetic studies indicate that, over the years, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

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

When the biologist marked frogs and attempted to find them in the subsequent week and a half, she could find just one marked frog from time to time, indicating their numbers were massive.

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

Deafening Noise and Rising Worries

The amphibians' proliferation is evident from the acoustic chaos they cause. "The number of frogs and the noise – it's really insane," says San José.

For the researchers, their nocturnal mating calls are helpful in determining their existence in remote areas, using recorders like the one outside the office.

But local agricultural workers say the sounds are so raucous they prevent sleep at night.

"In the rainy period, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a shock, observing the first frogs in the area," says the farmer, who started noticing their large numbers about several years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Stays Unclear

The sound isn't the primary problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for non-native organisms to thrive, as they have none of their natural predators. The islands counts 1,645 invasive types, many of which are significantly affecting the survival of its endemic ones.

A 2020 research indicates the invasive amphibians are hungry bug consumers, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or depleting the food sources of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Control Challenges

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

Their development stage is also highly variable, with some tadpoles turning into frogs very quickly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for six months.

"We really don't know this part," she says, worried the tadpoles could be impacting the islands' clean water, a very scarce resource in Galápagos.

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and slowly increasing the salinity of ponds in vain.

Research suggests spraying caffeine – which is extremely toxic to frogs – or using electrocution could assist, but these approaches aren't necessarily safe for other uncommon island organisms.

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

Funding Challenges for Research

While she expects the growing use of environmental DNA methods and genetic analysis will help her team make sense of the invasive species, financial support for the project has been difficult to obtain.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to control."