🔗 Share this article

On her daily commute to the research facility, biologist Miriam San José stoops near a shallow water body surrounded by thick plants and retrieves a small green sound device.

She had placed there overnight to record the characteristic croaks of the Fowler's snouted treefrog, known by local researchers as an non-native species with effects that experts are starting to understand.

Despite teeming with unique animals – such as ancient giant tortoises, swimming lizards, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had historically been free of frogs and toads.

During the 1990s, this changed. Several tiny tree frogs made their way from continental the mainland to the islands, probably as hitchhikers on transport vessels.

DNA studies indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm presence on several islands: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been struggling to keep track, calculating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the protected Galápagos national park.

When San José marked frogs and attempted to recapture them in the subsequent week and a half, she could locate just one tagged frog from time to time, suggesting their numbers were enormous.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

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

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

But nearby farmers say the sounds are so loud they keep them up at night.

"During the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, seeing the initial frogs in the region," says the farmer, who started observing their abundance about several years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

The noise isn't the primary problem, however. While the species has been in the Galápagos for nearly three decades, scientists still know limited information about its effect on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive organisms to thrive, as they have none of their enemies. The islands counts over sixteen hundred invasive types, many of which are significantly affecting the survival of its endemic ones.

A recent research suggests the non-native frogs are hungry bug eaters, and might be disproportionately eating uncommon bugs found exclusively on the islands, or reducing the nutrition of the islands' rare avian species, disrupting the food chain.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual characteristics, including living in brackish water, which is uncommon for amphibians.

Their development stage is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: the researcher observed one which stayed as a larva in her laboratory for six months.

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

Methods to control the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually increasing the salt content of ponds in vain.

Studies indicates spraying coffee – which is extremely toxic to frogs – or using electrical methods could help, but these methods aren't necessarily safe for other uncommon Galápagos species.

Lacking solutions to more of the basic questions about their lifestyle and effect, removing the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the increasing use of environmental DNA methods and DNA analysis will help her team make sense of the invader, funding for the research has been hard to obtain.

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