Which bird has a reversible outer toe to help it climb trees?

The story behind the answer

Woodpecker. Most woodpeckers have zygodactyl feet—two toes forward and two back—and an outer toe that can pivot backward, creating a clamp-like grip on vertical bark. Paired with their stiff, prop-like tail feathers, this foot design lets them brace and climb trunks while hammering for insects.

Remember it this way: woodpeckers are the carpenters of the bird world, and their “two-and-two” toes work like a carpenter’s clamp on wood. By contrast, nuthatches and treecreepers climb with long, curved claws but don’t have a reversible outer toe, and parrots use zygodactyl feet mainly for perching and manipulating food rather than trunk climbing.