Valley Forge National Historical Park officials say sharpshooters will start killing deer next month and end the first season in March, with a goal of killing 500 animals this winter. They say the park can support about 35 deer per square mile, and the current population is about 240 per square mile, or about seven times what it should be. Park managers say they need to thin a herd that has grown large and destructive, devouring young trees and other environmentally-sensitive vegetation. A contract with the federal agency that employs the sharpshooters calls for eliminating another 500 deer next winter, and 250 to 300 more in each of the last two years of a four-year-deal. They originally planned to start the deer kill last year, but they delayed it so they could review the contract and a lawsuit by animal-rights activists.