A two-year study could resolve a debate over the effect of Corolla's wild horses on prime waterfowl habitat.

The U.S. Fish and Wildlife Service plans to team with North Carolina State University to conduct exclosure studies within the Currituck National Wildlife Refuge to determine effects of large grazing mammals on three habitat types found there - maritime forests, marshland and wet meadows.

Wild horses graze on grasses also used by waterfowl for food and shelter, said Mike Hoff, manager of the Currituck National Wildlife Refuge. Migratory bird habitat takes precedence as the primary mission of the refuge, he said.

Set to start early next year, fenced areas in each habitat will exclude

either horses, feral hogs or deer to gauge the effect of each species, Hoff said.

One fenced area of 143 acres, already in place, excludes all three species and appears more lush than the surrounding area, Hoff said.

Meanwhile, the wild horse herd numbers about 100, 40 more than the maximum set by officials in a 1999 management plan. Setting a limit helps minimize the impact of hooves and grazing on the 4,570-acre refuge.

The Corolla Wild Horse Fund petitioned Fish and Wildlife last year to increase the herd size further to at least 120 to increase the gene pool and allow for a healthier herd.

The request was denied by Fish and Wildlife, but the herd limit of 60 has not been enforced over the years.

Wild horse experts have said a herd of 60 is too small, said Karen McCalpin, executive director of the Corolla Wild Horse Fund. A wild horse herd on Shackleford Banks remains about 120 on only 3,000 acres, she said.

The number 60 was chosen randomly without studies, McCalpin said.

"We don't have the level of scientific information to make educated management decisions on the horses," she said.

The Corolla Wild Horse Fund has attempted to reduce the herd. In the past three years, 35 horses have been removed through an adoption program, McCalpin said.

About 15 of the oldest and youngest mares have been darted with birth control serum. Over time, more of the 60 stallions must be removed to even out competition for the 40 mares, she said.

"There is so much fighting," she said.

DNA tests and other characteristics indicate that the Corolla wild horses descend from Spanish mustangs.

The horses roam through the 7,544-acre four-wheel-drive area of the Currituck northern Outer Banks, including the refuge and communities of beach rental homes and about 150 permanent residents.

At times, small groups leave the maritime forests and cross the dunes to the beach, drawing large crowds of people.

The horses are among the most popular tourist attractions on the Outer Banks.

In the summer, sales of wild horse T-shirts and hats help pay for horse management.

The study and others to follow are expected to show how many wild horses best keep the herd healthy and have a minimal effe ct on the refuge.

"There's probably a happy medium in there somewhere," Hoff said.

"We just have to find out what it is scientifically."

Jeff Hampton, (252) 338-0159, jeff.hampton@pilotonline.com