Hawaii's hated frogs: tiny invaders raise a big ruckus - populations of coquies, frogs native to Puerto Rico, invade Hawaii - Cover Story

Science News, Jan 4, 2003 by Janet Raloff

Puerto Rico's beloved mascot is a miniature tree frog named for its distinctive call: ko-KEE. All night long, choirs of love-starved males serenade would-be mates, who respond with quiet guttural chuckles. "To me, it's pleasant--just like birds singing," says Bryan Brunner, a University of Puerto Rico plant breeder in Mayaguez. "Here, everybody loves the coquies." And legend has it, he says, that coquies--native only to Puerto Rico--die of sadness when removed from their island.

Hawaiians are lamenting that that fable isn't true.

In the mid-1980s, potted plants from the Caribbean began arriving in Honolulu carrying frogs. Some were 5-centimeter-long coquies (Eleutherodactylus coqui), and others, a quieter and even tinier cousin, the greenhouse frog (Eleutherodactylus planirostris). These stowaways reveled in their new setting: a largely amphibian-free land with a bountiful smorgasbord of insects, tiny spiders, mites, and other delectables--and no snakes, tarantulas, or other natural predators.

By the end of 1998, seven populations of coquies had established themselves on the Big Island of Hawaii, recalls Earl Campbell of the Fish and Wildlife Service (FWS) in Honolulu. And the number has rocketed. "We now have over 400 populations on the Big Island," reports Campbell, the FWS Pacific Basin coordinator for invasive-species issues. He also notes a few coqui outposts on Maui, Kauai, and Oahu.

Local wildlife-protection officials have no trouble recognizing new coqui populations. On the Big Island, public officials receive about 10 complaints a day from homeowners who, unlike Puerto Rican residents, get fed up with the racket, notes Tim J. Ohashi of the Department of Agriculture's Wildlife Services Branch in Honolulu.

A backyard full of the frogs can reach 70 to 90 decibels--the volume of moderate-to-heavy street traffic or the din in neighborhoods along aircraft takeoff and landing corridors. Indeed, 75 decibels is the maximum sound volume that people can encounter at work throughout their careers without risking hearing loss (SN: 5/22/82, p. 347).

Hawaiians aren't used to such nighttime noise. "Because we don't have lots of calling insects, if you go to where the frogs aren't at night, it's dead quiet," observes herpetologist William J. Mautz of the University of Hawaii at Hilo. "Then enter an area with a big infestation, and you hit this wall of sound."

But it's not only the noise that has federal officials up in arms. The proliferating coqui and greenhouse frog populations on islands that evolved in the absence of amphibians threaten to overwhelm native ecosystems. That's why USDA has teamed up with the State of Hawaii and FWS to control--and, if possible, eradicate--the tiny hoppers.

The scientists are developing tools, including caffeinated sprays and scalding showers, for holding back what they see as an advancing plague of frogs.

HOPPING HATCHLINGS For the many frogs and toads that spend their youths as tadpoles, early survival and development depend on access to water in which they can swim and feed. But for members of Eleutherodactylus, the world's largest genus of vertebrates, young emerge from the egg or from Mom as tiny, fully formed frogs. This opens up a broader range of habitats than is available to tadpoles. Water-soaked moss decorating a potted plant will do, as will the humid packaging around plants, or a spoonful of water cupped in the leaf of an ornamental bromeliad.

Eggs, which coquies and greenhouse frogs lay on the soil, are hard to detect. Normally, male coquies guard their eggs for 2 to 3 weeks--not to fend off predators so much as to keep them moist, explains ecologist Larry Woolbright of Siena College in Loudonville, N.Y. Like a sponge, Dad's underbelly efficiently absorbs water and then releases it onto the eggs. But fatherless eggs could survive transit to Hawaii if they're attached to damp plant material, he says.

At hatching, baby coquies are green and only 5 millimeters long, about the size of a rice grain. Because they're nocturnal and don't begin bellowing their telltale serenades until they're about a year old, the youngsters tend to remain undetected, Woolbright says.

The frogs' catholic tastes facilitate their integration into the Hawaiian environment. After sleeping under leaf litter all day, the tiny amphibians come out after dark to dine. Some stay near the ground, while others ascend into a tree's canopy. Then they sit patiently and await the arrival of the evening's entrees--insects or any other small creature that crawls within pouncing range.

Hawaii's other Caribbean intruders, the greenhouse frogs, also concern scientists. So far, they've conducted relatively few studies of those quiet immigrants, which have proved difficult to find and count.

Though coquies invaded Florida roughly a century ago, they haven't spread far there, Campbell notes, probably because they had plenty of competitors for food and shelter.

But in Hawaii, he observes, "we don't have as many creatures as do ecosystems on the mainland, so we still have a lot of what people might term open niches." When the coquies and greenhouse frogs arrived, they set claim to one such niche.