The state has reported a 13-acre infestation of invasive coqui frogs near the Kuliʻouʻou summit in East Oʻahu.
The Department of Land and Natural Resources said the infestation is in a remote location with steep slopes inaccessible by foot, so crews plan to use drones to apply a non-toxic citric food additive mixed with water.
HPR talked with Division of Forestry and Wildlife information specialist Josh Atwood and coqui frog crew leader Ryan Chang to learn more about the eradication efforts.
"When they're down at low elevations, maybe they're not impacting too many native species, but to find them up at elevation in the summits of the Koʻolaus, that's really concerning for us as an agency concerned about the safety of our native species," Atwood said.
Many people think of coqui frogs as a residential pest whose noises make it hard to sleep, or as an agricultural pest in potted plants and nursery material. But Atwood said that studies show they can also eat invertebrates — like native tree snails.
There is no set date for dispensing the citric acid mixture, but Chang said late October would be the earliest. Crews are still testing the drone plan.
"People hear acid, and it sounds concerning, but this is a food additive, and so it's very safe for humans," Atwood said. "This is something that has been used on Hawaiʻi Island for a long time now, since they've unfortunately had coqui for a long time, and it's a very safe treatment product. It's deadly to the coqui only because they're amphibians."
Chang said a difficult part of eradicating coqui frogs is their nocturnal nature.
"That creates a challenge where we can't do helicopter operations at night at the moment, but with the drone, we can fly at night, and we can apply citric at night," Chang said.
The state learned of the Kuliʻouʻou coqui frog population from a member of the public who submitted a pest report. Various agencies then verified and surveyed the population.
"It's really important for the public to submit reports when they detect something that they think might be invasive in the wild," Atwood said.
He said state officials do not yet know how the coqui frogs got to the Kuliʻouʻou site.
Chang said that local biologist Patrick Hart and his team have been testing recording devices to analyze coqui frog colonies in nearby Waimānalo.
"We'll set them out before. We'll pull them back in, send the data over to Patrick Hart. And then after the treatment, we'll set them out again, and, you know, analyze it again, and then see if our treatment is effective. So if the densities go down and the calls go down, we'll continue with, you know, it being effective, and continue on that path," Chang told HPR.
Hart hosts HPR's Manu Minute — all about Hawaiʻi birds — and runs the LOHE Bioacoustics Lab at the University of Hawaiʻi at Hilo.
Kuliʻouʻou residents and hikers on the valley and ridge trails are encouraged to listen for frog calls. Pest reports can be submitted online at 643pest.org or by calling the 643-PEST telephone hotline.
Staff from DOFAW and OISC will be present at the Oct. 2 meeting of the Kuliʻouʻou Neighborhood Board to share information and answer questions about this project.
This interview aired on The Conversation on Sept. 26, 2024. The Conversation airs weekdays at 11 a.m. on HPR-1.
