The Galápagos Islands Lacked Any Native Amphibians. Then Countless Numbers of Amphibians Made Their Home

During her daily walk to the research facility, biologist the researcher stoops near a small water body covered by dense vegetation and collects a compact green audio device.

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

Although abounding with unique animals – including ancient large turtles, marine lizards, and the famous birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of Ecuador had historically been devoid of amphibians.

During the 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the islands, probably as stowaways on transport vessels.

DNA research suggest that, through time, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a firm foothold on two locations: Isabela and Santa Cruz.

The population is expanding so quickly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on each island, across urban and farming areas, but also in the protected natural reserve.

When San José tagged frogs and attempted to find them in the following 10 days, she could find only a single marked 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 pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they create. "The amount of frogs and the sound – it's really incredible," says San José.

For the scientists, their nightly mating calls are useful in determining their existence in remote areas, using audio devices like the one near San José's workplace.

But nearby agricultural workers say the calls are so raucous they keep them up at night.

"During the wet season, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.

"At first it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the species has been in the islands for nearly 30 years, experts still know very little about its effect on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very common for invasive species to prosper, as they have few of their natural predators. The islands has 1,645 invasive types, many of which are seriously disrupting the safety of its native ones.

A recent research indicates the non-native amphibians are voracious insect eaters, and might be disproportionately consuming rare bugs found exclusively on the islands, or depleting the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have exhibited some unusual traits, including surviving in slightly salty water, which is rare for amphibians.

Their development process is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a long time: San José observed one which stayed as a tadpole in her laboratory for half a year.

"We truly don't know this part," she says, concerned the larvae could be impacting the region's freshwater, a very limited commodity in the islands.

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

Research suggests applying coffee – which is highly toxic to frogs – or using electrical methods could help, but these methods aren't always secure for other rare island organisms.

Without answers to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of eDNA methods and genetic analysis will help her team understand of the invasive species, funding for the project has been difficult to come by.

"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 control."