🔗 Share this article

On her regular commute to the scientific station, biologist the researcher stoops near a small pond surrounded by thick plants and retrieves a small plastic sound recorder.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with effects that scientists are starting to understand.

Despite abounding with unique animals – including ancient giant tortoises, marine iguanas, and the well-known birds that sparked Charles Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had long remained free of amphibians.

During the 1990s, this shifted. Several tiny amphibians traveled from continental the mainland to the archipelago, likely as hitchhikers on cargo ships.

Genetic research suggest that, through time, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a firm foothold on several locations: multiple locations.

The numbers is growing so rapidly that researchers have been finding it difficult to monitor, calculating populations in the millions on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to recapture them in the following week and a half, she could find just one marked frog occasionally, 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 quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nocturnal vocalizations are useful in determining their existence in far-flung areas, using recorders like the one near San José's workplace.

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

"In the rainy period, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unclear

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

On archipelagos, it is very common for invasive species to prosper, as they have few of their natural predators. The Galápagos has over sixteen hundred introduced types, many of which are significantly affecting the safety of its native ones.

A recent research indicates the non-native amphibians are voracious bug eaters, and might be disproportionately consuming uncommon insects found only on the archipelago, or reducing the nutrition of the region's rare birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have shown some unusual traits, including surviving in slightly salty water, which is uncommon for frogs.

Their development stage is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a long time: San José witnessed one which remained as a larva in her lab for half a year.

"We truly don't know this part," she says, worried the larvae could be affecting the islands' clean water, a very limited commodity in the islands.

Techniques to curb the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by hand and slowly increasing the salinity of ponds in without success.

Studies indicates spraying caffeine – which is highly toxic to frogs – or using electrocution could help, but these methods aren't necessarily secure for other uncommon Galápagos species.

Without solutions to more of the basic issues about their lifestyle and impact, culling the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and DNA analysis will help her group make sense of the invasive species, financial support for the project has been difficult to come by.

"Everyone wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."