Twelve zoo-bred antelope released on a Texas ranch in 1930 have multiplied into tens of thousands, and now they threaten a border defense that took forty years to build. The nilgai, Asia’s largest antelope, escaped captivity because fences barely slow them down.
In the early morning hours along the Texas coast, a large animal stands motionless in the thorny brush near a farm road. It watches a passing truck. The creature stands about five feet tall at the shoulder, enough to look a driver in the eye through the window. Its coat is a dull blue-gray, nearly invisible in the dim light. The body is built for speed, with broad shoulders and a sloping back that…