Published: Thursday, Mar. 13, 2008 / Updated: Thursday, Mar. 13, 2008 12:40 AM

Officials want to use contraceptives to thin out squirrel population, stop spread of property damage

COLUMBIA -- Squirrel contraception: Once you get past the jokes, it makes sense.

Burgeoning gray squirrel populations are causing problems in urban areas. Shooting them in neighborhoods can be dangerous (and illegal in many municipalities). Poison would be socially unacceptable and hard to administer without harming other animals.

Searching for a solution, Clemson University researchers plan to try contraceptives.

Stop giggling. This is serious stuff. Clemson officials documented at least $1.3 million in squirrel-caused damages on the school's campus. Much of the damage is caused when squirrels gnaw bark off trees to mark their territory. But they also destroy wiring and duct work under houses and offices.

"There's got to be some (method) for cutting populations back," said Greg Yarrow, the Clemson wildlife ecology professor supervising the study.

The study, in conjunction with the U.S. Department of Agriculture's National Wildlife Research Center, will be done at the Clemson Experimental Forest and is designed to reveal the effectiveness of two methods of contraception.

The first, and most promising, involves trapping squirrels and injecting them with GonaCon, which renders males and females infertile. Because squirrels live only one to three years and generally stay within about a 3-mile radius, a thorough trap- and-inject program could greatly reduce populations for years.

Of course, hungry squirrels from nearby areas eventually would discover the underused food sources and move in. But that could take a while.

The other method involves food soaked in an oral contraceptive called DiazaCon. This is less promising because, like human oral contraceptives, it must be taken over and over, Yarrow said.

Squirrels that eat DiazaCon-coated food over a 10-day period should be infertile for about four months. To control the population in an area, you'd have to put out treated food for 10 days every four months.

The other problem with oral contraceptives is keeping the DiazaCon-coated food away from other creatures. The hot items in bird stores these days are squirrel-proof bird feeders. For the Clemson study, researchers are working on bird-proof squirrel feeders. They've come up with a tube design they think will do the trick.

Michael Williams of Camden let out a loud laugh when told about the subject of the research. A former state wildlife officer, Williams is regional director of the tongue-in-cheek organization Squirrels Unlimited.

"The best way to control squirrels is good trigger control," Williams said.

In neighborhoods where shooting isn't allowed, "they're real easy to trap, and you can relocate them," he said.

Williams used to have a squirrel problem around his house. Then, he got a couple of good squirrel dogs. The population in his yard thinned quickly.

Yarrow acknowledged that "a high-end pellet gun is more cost- effective" than contraception. But he said the Clemson study could provide another tool for use in special situations.