If I walk through a forest in Georgia, where I live, and fail to see or hear the pileated woodpecker, am I permitted to conclude that the bird is absent?

WSJ: The Brains of the Animal Kingdom

Even in the afternoon sun though, a short walk can easily lead you into perennial mist forest and over the trickle of a mountain stream.

BBC: Colombia��s valley of the palms

In the thick forest-savannah mosaic of northern Congo, many days' walk from any tarmac, your correspondent unearthed a milestone, half-buried in the leaf-litter, pointing to the small town of Badai, 15km to the east.

ECONOMIST: Seeing the wood