Genetic studies suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the frogs now have a strong foothold on two islands: Isabela and Santa Cruz. The population is growing so fast that scientists have been struggling to keep track, estimating numbers in the hundreds of thousands on each island, across urban and agricultural areas, but also in the protected Gal\u00e1pagos national park.<\/p>\n
When San Jos\u00e9 marked frogs and tried to recapture them in the following 10 days \u2013 a technique commonly used to make estimates of animal populations \u2013 she could find just one marked frog every once in a while, suggesting their populations were huge. They estimated 6,000 frogs in a single pond. \u201cOur estimates are still very conservative,\u201d says San Jos\u00e9. \u201cI am pretty sure there are even more.\u201d<\/p>\n
The frogs\u2019 abundance is clear from the acoustic chaos they cause. \u201cThe amount of frogs and the noise \u2013 it\u2019s really insane,\u201d says San Jos\u00e9.<\/p>\n
For the scientists, their nightly mating calls are helpful in estimating their presence in far-flung areas, using recorders like the one outside San Jos\u00e9\u2019s office. But local farmers say the calls are so raucous they keep them up at night.<\/p>\n
\u201cDuring the wet season, I constantly hear their calls and they\u2019re really loud,\u201d says Jadira Larrea Saltos, a coffee farmer at Finca La Envidia on Santa Cruz.<\/p>\n
\u201cAt first it was a surprise, seeing the first frogs in the area,\u201d says Larrea Saltos, who started noticing their abundance about three years ago when one jumped on her hand as she was walking out of her front door. Now she has more poultry on her property, which she thinks has helped keep the populations relatively at bay.<\/p>\n
The noise isn\u2019t the fundamental problem, though. While the species has been in the Gal\u00e1pagos for almost 30 years, scientists still know very little about its impact on the archipelago\u2019s delicately balanced land and water ecosystems.<\/p>\n On islands, it is very common for invasive species to thrive, as they have none of their natural predators. The Gal\u00e1pagos counts 1,645 invasive species, many of which are seriously disrupting the safety of its endemic ones. Avian vampire flies are bleeding rare bird hatchlings dry, and the hardy blackberry plant is encroaching on the Scalesia forests.<\/p>\n A 2020 study suggests the invasive frogs are voracious insect eaters, and might be disproportionately consuming rare insects found only on the archipelago, or depleting the food sources of the islands\u2019 rare birds, disrupting the food chain. Since the frogs\u2019 diet is dominated by moths, they could even be affecting pollination on the islands, according to ecologist Mar\u00eda del Mar Moretta-Urdiales, who was involved in the study.<\/p>\n The Gal\u00e1pagos frogs have exhibited some unusual traits, including living in brackish water, which is uncommon for amphibians. Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very quickly and others taking a long time: San Jos\u00e9 observed one which remained as a tadpole in her lab for six months.<\/p>\n \u201cWe really don\u2019t know this part,\u201d she says, worried the tadpoles could be affecting the islands\u2019 freshwater, a very scarce resource in Gal\u00e1pagos. And even though studies show that the Gal\u00e1pagos diving beetle now eats large numbers of tadpoles in its diet, it doesn\u2019t seem to be making a dent in their populations.<\/p>\n Methods to curb the frogs in the early 2000s were largely unsuccessful. Park rangers tried capturing large numbers by hand and gradually increasing the salinity of lagoons in vain. Research suggests spraying coffee \u2013 which is highly toxic to frogs \u2013 or using electrocution could help, but these methods aren\u2019t necessarily safe for other rare Gal\u00e1pagos species.<\/p>\n Without answers to more of the basic questions about their biology and impact, culling the frogs might not even be the right way to go, says San Jos\u00e9.<\/p>\n While she hopes the growing use of environmental DNA techniques and genetic analysis will help her team make sense of the invader, funding for the project has been hard to come by. \u201cEverybody wants to give funding for preserving frogs,\u201d says San Jos\u00e9. \u201cBut it\u2019s harder to find funding for an introduced frog that you might want to control for.\u201d<\/p>\n