Agency plans to eradicate frogs on Kaua'i

By Jan TenBruggencate
Advertiser Kaua'i Bureau

The Caribbean coqui frog has been found on Maui, the Big Island, O'ahu and Kaua'i. Federal officials are planning to eliminate the noisy frogs on Kaua'i before they spread. Advertiser library photo

The frogs, whose nighttime chirps are described as being as loud as a chainsaw at more than 70 decibels, keep residents awake with a call that sounds like their names: "ko-KEE." The Caribbean frogs were first heard in the Islands in 1992, and are now found on the Big Island, Maui, O'ahu and Kaua'i. They are so widespread in some areas, covering hundreds of acres, that their removal may be impossible.

But authorities feel that there is hope on Kaua'i.

"We think there are less than 100 of them, in about three acres," said John Eisemann, wildlife biologist with the U.S. Department of Agriculture's wildlife services branch in Hilo. He is heading up a project to try to remove the Kaua'i population of the frogs before they spread.

The agency is working with the state Department of Agriculture, state Department of Land and Natural Resources, University of Hawai'i and the Kaua'i Invasive Species Committee. Crews will take hoses from tanks of citric acid into the area during the next two weeks, and drench the vegetation. They will return for several nights to listen for surviving coqui calls and treat those areas from backpack sprayers. Afterward, they will depend on neighbors — who would be awakened by the calls — to report any new infestation.

Eisemann said federal Department of Agriculture crews were surveying the Lawa'i gully where the coqui are found, and preparing pathways from which they can spray the citric acid. Officials used caffeine as a control agent for a time, but federal registration of the compound for use on frogs expired. Citric acid is considered sufficiently benign that no federal approval is needed.

The acid compound, a little stronger that lemon juice, has no effect when applied to unbroken human skin, but it quickly kills the frogs and their eggs, Eisemann said. It can cause some spotting on plants, but does not kill them, he said.

The agriculture agency is using the Lawa'i project as a test case, setting out insect, lizard and gecko traps before and after the treatment to see how it affects their populations. It is also testing soil and water nearby to see if there is any effect from the citric acid spray.

"We expect the populations of invertebrates (like insects) to drop during the first week and then return to normal. The data will go into an environmental assessment" that could allow the federal agency to participate in similar eradication efforts in other locations later, Eisemann said.

The Po'ipu area of Kaua'i also has an infestation of the coqui's cousin, the greenhouse frogs. Federal agricultural officials are treating the resort area with citric acid to try to control these frogs in dark, wet areas where they congregate.

Greenhouse frogs chirp, but are considerably quieter and smaller than the coqui. While the coqui fits on top of a quarter, the darker greenhouse frog fits on top of a dime. Both species of frogs need a moist environment, but they do not need standing water. Neither has a tadpole stage; they hatch from eggs.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.