Galápagos Had No Native Amphibians. Until Hundreds of Thousands of Amphibians Made Their Home

During her daily commute to the research facility, biologist the researcher stoops near a shallow water body covered by thick plants and retrieves a compact plastic audio recorder.

The device was left there overnight to record the distinctive calls of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that experts are just beginning to comprehend.

Although abounding with remarkable animals – such as ancient large turtles, marine lizards, and the famous finches that sparked Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been free of frogs and toads.

During the 1990s, this shifted. Some tiny amphibians made their way from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic research indicate that, through time, there have been multiple accidental introductions to the islands, and the frogs now have a firm presence on several islands: Isabela and Santa Cruz.

The population is growing so quickly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to find them in the following 10 days, she could find only a single marked frog occasionally, indicating their populations were massive.

They estimated six thousand frogs in a single pond. "Our estimates are still very low," says San José. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nightly mating calls are helpful in estimating their existence in remote areas, using audio devices like the one outside San José's office.

But nearby agricultural workers say the calls are so loud they prevent sleep at night.

"In the rainy period, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

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

Environmental Consequences Stays Unclear

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive organisms to prosper, as they have none of their enemies. The Galápagos counts over sixteen hundred invasive species, many of which are significantly disrupting the safety of its native ones.

A 2020 study suggests the invasive frogs are voracious bug eaters, and might be disproportionately eating rare insects found exclusively on the islands, or reducing the food sources of the region's rare avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some atypical characteristics, including surviving in brackish water, which is uncommon for amphibians.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a tadpole in her laboratory for half a year.

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

Techniques to control the frogs in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by manual methods and slowly increasing the salt content of ponds in without success.

Research suggests spraying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily secure for other uncommon island species.

Without answers to more of the basic questions about their lifestyle and impact, culling the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will assist her team make sense of the invasive species, financial support for the research has been difficult to come by.

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