If you live in coqui frog country and are pleased that the nighttime noise has diminished, get the earplugs ready.

The din of coqui calling tapers off in the winter but picks up again as the weather warms, according to Rachel Neville, outreach specialist with the O'ahu Invasive Species Committee.

When people go out to try to control coqui populations, they generally go out at night and try to locate them by the calling. Only male coqui make the characteristic two-toned chirp; when they're not calling, it's hard to find the little frogs, which are tiny enough to fit on the top of a quarter.

Neville said that as residents start hearing the frogs calling in earnest again, they can call a statewide pest hot line at 643-7378. Teams from the state Department of Agriculture, state Department of Land and Natural Resources and the invasive species committee for that island will respond or provide information to residents.

If you're not sure what you're hearing is a coqui, you can listen to a recording of the frog's call at the O'ahu Invasive Species Committee at www.oahuisc.org or the Hawai'i Ecosystems at Risk project Web site, www .hear.org.

It's a good idea to check, to be sure it's not a cricket or another kind of frog you're hearing. The smaller and slightly quieter greenhouse frog is often mistaken for its cousin. On O'ahu, in 2005 only 14 of 95 reports turned out to be coqui. And so far this year only four of 25 have been coqui.

The animals are widespread on Maui and the Big Island, are found in a small pocket in Lawa'i on Kaua'i, and are in several populations on O'ahu, the largest in a forested area in Wahiawa.

Coqui, Eleutherodactylus coqui, are beloved in their native Caribbean but are considered an invasive species in the Hawaiian Islands. They differ from some other frogs in that they don't need standing water to thrive and reproduce. They were accidentally introduced in the 1980s, apparently in a shipment of nursery plants. There are Hawai'i residents who argue for allowing the frogs to remain and spread, suggesting their impact on the environment is not significant.

A variety of compounds has been used to try to control them, including caffeine, agricultural lime and, most recently, citric acid. O'ahu officials reduced the population of the frogs in Wahiawa by drenching the area with citric acid in 2005 but did not wipe them out. They plan to try again this summer, when the noise level helps indicate where the frogs are.

If you have a question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate at P.O. Box 524, Lihu'e, HI 96766 or jant@honoluluadvertiser.com. Or call him at (808) 245-3074.