The Hawai'i Voices of Science episodes tell natural resource stories on Hawai'i Island.
A noisy little amphibian is causing quite the ruckus on Hawaii Island - the invasive coqui frog. Coming all the way from Puerto Rico, the coqui frog has invaded Hawai’i Volcanoes National Park. Coqui threaten the native ecosystems and shatter the natural soundscapes in the park. But The Coquistador is on the case! Biological Resource Technician Kim Dilman works by night, removing frogs from the landscape to protect sensitive areas and preserve the native, natural resources in the park.
Voices of Science: The Coquistador
Coming all the way from Puerto Rico, the coqui frog has invaded Hawai’i Volcanoes National Park. The park is working hard to protect the native, natural resources in the park.
Jennifer Jerrett: So when you look at that, what do you see?
Kim Dillman: When I see it? I just see a frog. A noisy little frog (laughs).
Narrator: For the National Park Service, I’m Brittni Connell, and you’re listening to Voices of Science.
Kim: So, I just caught one. He was over there on the ginger. They love this kind of vegetation… this is kind of how they hang out. You have a search image.
Narrator: This is Kim Dillman, Biological Resource Technician for Hawaii Volcanoes National Park. And tonight, Kim is talking about getting a search image for frogs. Hawaii’s invasive Coqui frog. Kim holds the frog by the leg and shines her headlamp so we can get a better look.
Kim: They come in different colors of orange and brown, tan ... sometimes they're really dark and mottled, and sometimes they sort of change their color, depending on the vegetation that they're in.
Narrator: Kim puts the frog in a plastic bag and marks the tree with some flagging. She zeroes in on another frog that’s calling.
Kim: Oh, oh, that's a biggie! Okay. And you can see him blowing up his throat, too, when he calls. Can you see him?
Narrator: In the past few years, coqui populations have exploded. Lower elevation areas have been hit the hardest, but the infestation is steadily marching upslope toward Kilauea. Kim is mapping the spread of the frogs inside the park and she’s working hard to prevent them from moving into areas that are currently coqui free. When she finds infested areas, Kim traps the frogs or sprays a solution of citric acid to kill them. People around here have a special name for her.
Kim: Oh, the Coquistador? (laughs) I’m just the coqui lady. I’m just the frog lady around here. (laughs)
Narrator: Twenty years ago, the first coqui frogs hitched a ride to the islands on some potted plants then dispersed into the native forests. Because they are prolific breeders, the frogs quickly invaded the ecosystem. Now the park is trying to eradicate the coqui partly because their loud calls have become a big problem for the island’s residents.
But when you hear them for the first time, that can be hard to understand.
David Benite: It is worth mentioning that in their home range in Puerto Rico, they are cherished...
Narrator: That’s David Benitez. Ecologist at Hawaii Volcanoes National Park. For the past 16 years, David has been monitoring invasive species in the park. He says there’s a dramatic difference between the native populations of coqui frogs in Puerto Rico, and the nonnative populations here in Hawaii.
David: The difference is that there, they're part of the ecosystem. They evolved there and they tie into the food web. They're food and prey for snakes and lizards and they serve a purpose. Here, it's a different story. Here, there are no ground dwelling mammals, no snakes, no frogs, nothing that could really directly compete with or predate on Coqui frogs. As a result, they can, they thrive and flourish here and achieve densities roughly three-fold what they do in their native Puerto Rico.
Narrator: It’s estimated that in Hawaii coqui populations can reach densities of up to 50,000 frogs in an area about the size of one city block. David says the sound of thousands of frogs in a relatively small area like this can be intense. This is a pretty big change from the quiet nocturnal soundscape that Hawaii was once known for.
David: And Coqui frogs shatter that quiet in their invaded habitats...They so dramatically, alter the soundscapes.
Narrator: Hawaii’s ecosystems evolved in extreme isolation. That isolation created insects and birds and other animals that are simply found nowhere else on earth. And those species? They evolved in a nocturnal soundscape without frogs. Soundscapes where they could use sound to communicate with each other and to sense what was going on around them.
Now, with the native nocturnal soundscape drowned out by the coqui chorus, it’s harder for those animals to hone in on their familiar sound cues. Sound cues that are critical for survival.
David: Research also suggests that the Coqui frogs achieve such a density that they alter ecosystem properties, mainly the nutrient cycling in the invaded forest.
In turn, those changes in nutrient cycling may further favor invasion by other plants and animals, contributing to further degradation of the system.
Narrator: Coqui frogs are also voracious eaters.
David: And that's a problem for the native insect communities and also the species that depend on those insects for pollination or for food such as the native birds of Hawaii.
Kim: We have special ecological areas, where they try to keep all the vegetation native, and we’re also trying to prevent the coqui from getting there. Those are the areas that we can do something about, because they're not infested yet.
Narrator: Holding back the tide of the tiny frog with the big voice seems like an impossible job. But for Kim, the effort is worth it.
Kim: I remember what it sounded like before we had coqui. It was pretty cool to be out here and just listening to the night sounds before. Now, you come out here at night, and you just listen to coqui.
There's never a point where it just stops and just gets quiet. Because some frogs will stop; the other ones will start up and it just keeps going all night long. It kind of makes you tired, having to listen to these frogs all of the time…
I love this park. It's not that I don't like the coqui in the park. It's just I love the park. I like it to be natural and native...so, yeah I'm trying to protect this legacy for the people who appreciate it, or who haven't been able to experience it yet. I want them to be able to experience as much of it in a natural state as possible. A native, natural state.
Narrator: Voices of Science was produced by the National Park Service in cooperation with the Acoustic Atlas at Montana State University.
Our staff includes Jennifer Jerrett, David Restivo, Sara Melena, and me, Brittni Connell.
Special thanks to Jacob Job at Colorado State University. And to Jessica Farracane, Kim Dillman, and David Benetiez at Hawaii Volcanoes National Park at nps.gov/havo. Find more episodes of Voices of Science at go.nps.gov/voc. Thanks for listening.