NANAWALE FOREST RESERVE — In the heart of coqui country, researchers are trying to figure out what makes the frogs sing.

Much of the research done so far on coqui frogs involves studying ways to kill them. Emily Price, a 28-year-old doctoral candidate in ecology, is part of a team that is studying, in a broad way, how humans and frogs interact.

"I've always been interested in invasive species," Price said in the parking lot of the Lava Tree State Monument, near one of the study sites in the Big Island's Puna district.

While studying at Utah State University, Price came across Eleutherodactylus coqui in a listing of the world's worst invasive species, and was intrigued.

The frogs are native to Puerto Rico, where they're beloved for their chirping sounds. There is — or was — a myth that coquis won't chirp once they're taken away from Puerto Rico.

Irritated Big Island residents know otherwise, and they've taken sometimes drastic measures to quiet the frogs.

In December 2008, Price arrived in Hawai'i and began conducting in-person interviews with 87 residents around Hawai'i County about their attitudes toward the frogs.

Price also developed a mail survey and sent out 2,000 copies to landowners across the Big Island and another 2,000 collectively to Maui, Kaua'i and O'ahu.

The survey asks such questions as: In the last 12 months, have you removed a plant because coquis seemed to like it? Have you introduced an animal to your property to manage the coqui? How much have you spent, in total, to manage the coqui?

The survey also asks for opinions on use of chemicals to manage the coquis, the importance of interacting with neighbors, and what methods — spraying, dusting and catching, among them — are used to keep the chirpers away.

The overall goal is to determine what factors make a property more or less attractive to coqui frogs, said Mark Brunson, the project's principal investigator, speaking by phone from Utah State. How much do varying levels of mulch, undergrowth and insect population affect the coqui populations? And how is that related to what property owners know or do?

That is why, since last December, Price and several others have lived in a rented house in Puna, working in the forest reserve.

"She's basically doing the biology and one of the things that makes her doctoral research unique is that it's both the biology and psychology," Brunson said.

While other researchers might separate the study of the coqui frogs and the humans who live among them, Price is integrating the two disciplines.

She's studying the dispersal of frog populations, Brunson said. What happened when you changed the amount of litter on the ground? How is that related to the numbers of frogs? How is that related to the insects?

After getting the necessary permits from the state, Price set up four work sites in the forest reserve, each 20 by 20 meters (about 66 feet on each side). Each of the sites was then divided into five plots, and different ground treatments were used in each plot.

For example, Price is testing the hypothesis that removing all the leaf litter from the ground would reduce the number of frogs.

For about two weeks in February and March, the team was on hands and knees, scooping a total of 20,000 pounds of plant and leaf litter into garbage bags and carrying it out. The team set up insect glue traps to gauge the amount of flying frog food in the area.

Then, on selected nights, the team dons headlamps and over several hours attempts to count the frogs they see.

There are a lot of frogs in lower Puna, somewhere on the order of one per square foot.

Some nights they catch the frogs, clip tiny tags to their toes and release them for recapture later.

"There has been a difference in the frog population by altering the resources," Price said.

The goal, she said, is "to be able to determine what are the influences on coqui density. Is it people's attitudes? Land management? Behavior? Habitat?"

Price hopes to publish the results in an academic journal and perhaps make a public presentation in Hawai'i.