(Gettysburg) -- The National Park Service will resume its annual effort to thin the deer herd at the Gettysburg National Military Park and Eisenhower National Historic Site. Starting next month, qualified federal employees will shoot the animals at night in closed sections of the park. Park spokeswoman Katie Lawhon says it is not a "hunt." She says on the battlefield, deer have no natural predators and an abundance of food, so their numbers multiply rapidly. "Until something changes, we foresee that we'll always have to manage the deer. We'll always have to do something to try to keep it somewhere close to our goal, which is to have 25 deer per square mile of forested habitat," Lawhon says.  She says the park service has killed between 100 and 150 deer each year for the past five years.  The deer management program began in 1995 with the goal of protecting the park's vegetation and farmland. The venison will be donated to food banks in the region.