Encouraging signs but no woodpecker

Birders searching a Louisiana forest this winter for the long-lost ivory-billed woodpecker heard a knock-knock and would dearly love to know who’s there.

The ivory-billed woodpecker, with its 31-inch wingspan and 20-inch length, hasn’t been documented in the United States since the 1940s, and observers haven’t confirmed the existence of the Cuban subspecies since the 1980s.