🔗 Share this article The Galápagos Islands Had No Native Amphibians. Then Countless Numbers of Frogs Made Their Home During her regular commute to the scientific station, scientist Miriam San José stoops near a shallow pond surrounded by thick vegetation and collects a compact green audio device. The device was left there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by local scientists as an invasive species with consequences that experts are starting to understand. Despite teeming with unique wildlife – such as ancient giant tortoises, swimming iguanas, and the well-known finches that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had historically been free of amphibians. In the late 1990s, this shifted. Several tiny amphibians traveled from continental Ecuador to the islands, likely as hitchhikers on cargo ships. The invasive species came in the 1990s and have taken hold on Isabela and Santa Cruz islands. DNA studies suggest that, through time, there have been multiple unintentional arrivals to the islands, and the frogs now have a strong foothold on several locations: multiple locations. The numbers is expanding so quickly that scientists have been struggling to keep track, estimating numbers in the millions on every island, across urban and agricultural areas, but also in the protected natural reserve. When San José marked amphibians and attempted to recapture them in the following 10 days, she could locate only a single marked frog occasionally, suggesting their populations were massive. They calculated 6,000 frogs in a single pond. "Our estimates are still very low," states San José. "I am quite certain there are additional numbers." Deafening Noise and Growing Concerns The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's truly insane," says the scientist. For the researchers, their nightly mating calls are helpful in estimating their existence in remote areas, using recorders like the one outside the workplace. But local agricultural workers say the sounds are so raucous they keep them up at night. "In the rainy period, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz. "At first it was a shock, observing the first frogs in the area," says Larrea Saltos, who started observing their large numbers about several years ago when one leaped on her hand as she was walking out of her front door. Ecological Impact Remains Unclear The noise isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, experts still know limited information about its effect on the islands' delicately balanced land and water environments. Researchers are finding out more about the amphibians, including that they can remain as larvae for as long as half a year. On islands, it is very typical for non-native species to thrive, as they have few of their natural predators. The islands counts over sixteen hundred invasive species, many of which are significantly disrupting the safety of its endemic ones. A 2020 study indicates the invasive frogs are hungry insect eaters, and might be unevenly eating rare insects found only on the islands, or depleting the nutrition of the region's rare avian species, affecting the ecosystem balance. Unusual Traits and Control Challenges The Galápagos frogs have exhibited some unusual characteristics, including living in slightly salty water, which is rare for frogs. Their development process is also highly variable, with some larvae becoming frogs very rapidly and others taking a long time: San José witnessed one which stayed as a tadpole in her lab for six months. "We truly don't know this aspect," she says, worried the tadpoles could be impacting the region's clean water, a very limited resource in Galápagos. More research is required to determine the best way to control the frogs without affecting other organisms. Techniques to curb the amphibians in the early 2000s were largely ineffective. Conservation officers tried collecting large numbers by hand and gradually increasing the salinity of ponds in vain. Studies suggests applying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos species. Lacking solutions to more of the fundamental issues about their biology and impact, culling the amphibians might not even be the right way to advance, says the biologist. Funding Challenges for Research While she hopes the increasing use of eDNA techniques and genetic analysis will help her team make sense of the invader, funding for the research has been difficult to obtain. "Everyone wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find financial backing for an invasive frog that you might want to control."