The Coqui Frog - A Continuing Saga in Hawaii

What creature is no bigger than an American quarter – and has a piercing continuous chirp, rivaling the sound of a chainsaw, from dusk until dawn? It’s the coqui frog (Eleutherdactylus coqui), a tree frog native to Puerto Rico, that made its way to Hawaii as an accidental passenger on imported plants. These frogs have come into Hawaii and they’ve produced population explosions. They get densities up to three times what have in their native habitat of Puerto Rico. Densities like two to three frogs for every square yard of forest, says biologist Bill Mautz at the University of Hawaii in Hilo.
Mautz says the coqui devour huge numbers of spiders and insects. And he worries about their potential to compete with birds and other critters who depend on the same food sources. The majority of Hawaii’s native forest birds are partially or entirely dependent on insects for food. If coqui and greenhouse frogs spread to forest bird ranges, the frogs could out-compete native, endangered species.
At peak densities in Puerto Rico, coqui frogs, with their voracious appetites, can consume 47,500 prey per night per acre. Because these frogs consume such an abundance of insects, biologists are also concerned that they could lead to the extinction of Hawaiian arthropods like native spiders, which have already been negatively affected by the establishment of other invasive predators.
Caribbean tree frogs (such as the coqui and the greenhouse frog) are primarily nocturnal, seeking shelter during the day in moist areas covered by brush or debris. They prefer hot, humid environments that receive lots of rain. Since first being seen in Hawaii in 1992, the coqui frog and the greenhouse frog (E. planirostris) have been a threat to the state’s agriculture, tourism, and native ecosystems. With its tropical climate and a lack of natural predators, Hawaii has become a perfect second home to these invasive species. Both species are light-brown to dark or reddish in color and have variable patterns, including light stripes down the back.
The coqui frog, known for its piercing chirp, is much easier to detect than the quieter greenhouse frog. Coqui have been reported at more than 320 locations covering approximately 2,000 acres on the islands of Hawaii, Maui, Oahu, and Kauai.
Mautz said coqui frogs are extremely loud. "We’ve measured sound pressure levels up around 73 decibels. That’s around like a loud party. You’ve got to raise your voice to have a conversation in the middle of that." Beginning at dusk and continuing until dawn, male coqui frogs move into the trees and call “ko-kee” over and over to attract females. Many residents and tourists have experienced sleepless nights as a result of the incessant chirping of the male coqui frog.
People have tried various frog remedies to alleviate the problems caused by the coqui. There’s research going on regarding other means of chemical control -- including hydrated lime to control coqui frog populations. There’s research on possible biological control methods. But so far there’s no magic bullet on the immediate horizon.
In an effort to protect Hawaii’s natural resources and preserve the islands’ inherent tranquility, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) is working to develop environmentally sound strategies to manage coqui and greenhouse frog populations. Scientists at APHIS’ National Wildlife Research Center (NWRC) Hawaii field station in Hilo, in cooperation with the State Department of Agriculture and the University of Hawaii’s College of Tropical Agriculture and Human Resources, have already discovered several promising new methods.
The product currently being tested is commonly used as a soil amendment to reduce acidity. It is called slaked lime or calcium hydroxide. It is cheaper and in some ways easier to use than the other common coqui frog-control chemical, citric acid, said Kyle Onuma, the state Department of Agriculture weed specialist in Hilo, Hawaii. Onuma figured out that hydrated lime might work. He used lime when he grew ginger commercially, and recalled that if it got on his skin, he would feel a burning sensation if he sweated. Since coqui frogs have moist skin, he though it might work against the animals. It did. Both citric acid and hydrated lime attack the frogs' skin and cause death within a short time, he said.
Whatever the end result, conservationists need to be aware of the effects of the coqui -- and the effects on coqui populations.

Original source: Earth and Sky

Other Coqui Resources:
ScienceNews - "Hawaii's Hated Frogs"
University of Hawaii at Manoa - Coqui research
APHIS.USDA.gov - Coqui Information
Honolulu Advertiser - Coqui article
Hear.org - Coqui Flyer (pdf)
To Puerto Rico - Coqui Info