It's the dinner hour on Tuesday night, and Luanne Johnson is tromping through poison ivy and switch grass on the duney hills of Aquinnah's north shore, holding a fold-out antenna in one hand, a receiver in the other and hoping she will find her quarry: a skunk named Pua.

Ms. Johnson, who is researching Island skunks for her doctoral dissertation in environmental studies, has put radio collars on nine skunks, but four of them have already died.

This is not an anomaly. The fact is, the Island's skunk population is way down. Rodent trappers and other scientists who keep an eye on Vineyard wildlife are seeing the same thing: fewer skunks, less roadkill and a whole lot less stink.

That may be welcome news for homeowners, dog owners, shorebirds and just about anyone who has ever come within 10 feet of a skunk's spray, but there is some disagreement among the experts about the cause of the population dip.

"The winter devastated them," said Walter Wlodyka, a licensed skunk trapper in Chilmark.

"You have an incredible amount of mortality because of the winter," said Gus Ben David, director at the Felix Neck Wildlife Sanctuary in Edgartown. "Hundreds and hundreds died in the dens. With that prolonged snow cover and their little short legs, they had no intake of food. They used their reserves up."

Ms. Johnson, who is in her second year of studying Island skunks as part of her research at Antioch New England Graduate School, called the winter theory bunk.

"Skunks live in Canada and North Dakota," she said. "Do we have a winter? These guys had a break in January when it was 50 degrees. This has nothing to do with skunks having short legs and [being unable to] navigate through snow."

Ms. Johnson believes the skunks have fallen ill with some kind of disease. "It's definitely an epizootic of some sort," she said. "You have a population that's big for an epizootic to spread through. People in dense populations end up with more disease."

She has ruled out distemper and rabies, adding that tests have come up negative.

Lacking any hard scientific evidence, Ms. Johnson is now awaiting the results of a necropsy on a skunk carcass she sent to the University of Connecticut veterinary diagnostic lab in Storrs, Conn. They will analyze tissue samples and look for lesions on the brain and other organs.

"It could be anything," said Ms. Johnson, who now spends five to six nights a week tracking the sleep and living habits of five skunks between Chappaquiddick and Dogfish Bar in Aquinnah.

"It could be a tick-borne illness like babesiosis or tularemia or toxoplasmosis. They gave me a list a mile long of the possibilities," she said.

Mr. Ben David conceded that disease could be the culprit, but only because he believes the winter of snowstorms and cold temperatures weakened the skunks.

"You may have a combination of factors. When you get a stressed out population from the weather, that's not unusual," he said. "All their research will come back inconclusive. They're not going to find a sole pathogen."

Vineyard skunks, he added, cannot be compared with their brethren farther north. "It's two different gene pools. Those populations have evolved at that latitude," Mr. Ben David said.

Mr. Wlodyka argued hard that the raccoons are pillaging skunk habitats and food supplies.

"There's probably 10 or 15 raccoons for every skunk on this Island. They're faster, stronger, smarter, and they're taking over skunks' territory. Between the winter and the raccoons, there's little hope for the skunks," he said.

Ms. Johnson is equally quizzical about that theory, asking if the winter was so hard on the skunks, then how did the raccoons flourish? "That's not plausible to me," she said. "The raccoons are through the roof."

While there are battling hypotheses over the cause, no one disputes that the once dominant skunk battalions on the Island are now significantly thinned.

Sam Telford, an associate professor of infectious diseases at Tufts University who has been researching lyme disease and tularemia on the Vineyard, was unable to trap even one skunk two weeks ago when he and his team visited the Island. In April and May combined, they trapped just two skunks, Mr. Telford said.

Litter sizes are also down. "You're not going to see litters of ten. I'm seeing three or four," said Ms. Johnson.

T.J. Hegarty, the county rodent control officer, said skunks are now a rare sighting. "I've seen a real decline and the animals I saw in the spring had a lot of mange," he said. "I don't see the roadkill."

Even at The Bite, the clam shack in Menemsha notorious for the skunks that visit diners at the outdoor picnic tables, there hasn't been a single skunk sighting this season. And the surprising thing is, the owner is feeling nostalgic.

"They normally come out around Father's Day but I haven't seen one skunk yet," said Jackie Flynn-Morgan, a co-owner at The Bite. "I'm surprised. Personally, I miss them."

Meanwhile, Ms. Johnson is continuing her nightly treks into what remains of skunk country. Her five tagged skunks are programmed into a palm pilot: Along with Pua, there's Donna, Chuck, Mel and Ki.

Like most biology field research, it is a matter of recording all the details and being willing to get dirty. When she finds Pua's den Tuesday night, the main task involves collecting scat samples, taking a slotted spoon and pouring the fecal matter into a small zip-lock plastic bag.

"This is my little life, diving for skunk poop," said Ms. Johnson, smiling as she deposited samples in the bag.

She analyzes the scat to learn about the skunk's diet. The menu has forced Ms. Johnson to branch out into entomology.

"There's June bugs, wasp wings, bees, flying ants. They also eat tent caterpillars. I find a lot of wings and wing parts," she said.

Locating the skunks with her antenna and receiver is just like a game of hotter-colder. She listens for the frequency of a beeper and adjusts her direction. But she knows Pua's den by now and is actually pleased by the amount of scat she finds.

"Pua has been eating well. That's good," she said. "I've definitely seen some skunks not looking so healthy."

After decades of Islanders complaining about skunks, this appears to be the summer when the Vineyard's malodorous mascot begins to wane.

"Just goes to show that Mother Nature sometimes has its own way of dealing with an imbalance in numbers," said Mr. Telford.

But don't start counting on the Vineyard air staying fresh and scent free. The population may be the lowest in decades, said Mr. Ben David, but this drop is just a blip on the radar.

"The ones left that do survive . . . will come through and will have exceedingly large litters," he said. "I've been watching this stuff all my life and know the habits of the animals. The skunks, they'll come back."