🔗 Share this article

On her daily commute to the research facility, biologist Miriam San José stoops near a shallow water body surrounded by dense plants and collects a small green audio recorder.

The device was left there overnight to capture the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native threat with effects that scientists are just beginning to understand.

Despite abounding with unique wildlife – such as ancient giant tortoises, marine lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the island chain off the coast of South America had historically been devoid of amphibians.

In the late 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the islands, likely as stowaways on transport vessels.

DNA studies suggest that, through time, there have been repeated accidental arrivals to the islands, and the amphibians now have a strong foothold on several islands: Isabela and Santa Cruz.

The population is growing so rapidly that researchers have been struggling to monitor, estimating populations 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 recapture them in the following 10 days, she could find only a single marked frog from time to time, suggesting their populations were enormous.

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 Rising Worries

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

For the researchers, their nocturnal mating calls are useful in determining their existence in far-flung areas, using recorders like the one outside San José's office.

But local farmers say the sounds are so raucous they keep them up at night.

"During the rainy period, I constantly 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 area," says Larrea Saltos, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, however. While the species has been in the Galápagos for nearly three decades, experts still know very little about its effect on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very typical for invasive organisms to thrive, as they have few of their natural predators. The islands counts over sixteen hundred invasive species, many of which are seriously affecting the survival of its endemic ones.

A 2020 research suggests the non-native frogs are hungry insect consumers, and might be unevenly eating rare bugs found only on the islands, or reducing the food sources of the region's uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island amphibians have exhibited some atypical traits, including surviving in brackish water, which is uncommon for amphibians.

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

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

Methods to curb the amphibians in the beginning of the century were largely ineffective. Park rangers tried capturing large numbers by hand and gradually raising the salinity of lagoons in without success.

Studies indicates applying caffeine – which is extremely toxic to frogs – or using electrocution could help, but these approaches aren't always secure for other rare Galápagos species.

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

Financial Obstacles for Research

While she expects the increasing use of eDNA techniques and genetic analysis will assist her team understand of the invader, financial support for the project has been hard to come by.

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