On a recent snowy evening, Mr. Ehlert stopped his van near a derelict U.S. listening station on a hilltop in former West Berlin. During the Cold War, the U.S.'s National Security Agency eavesdropped on the Soviet bloc from here. Now the hill is crawling with boars. One by one, they emerged from the trees, grunting in expectation, until 15 plump hogs surrounded the van. "Someone is clearly feeding them," says Mr. Ehlert. That's illegal, because it leads to inappropriate boar-human mingling.