Question

why are the birds called expert thermal climber

Answer 1

No bird is better adapted for climbing up a tree trunk than a woodpecker. Its foot design is ideal for clinging, with two toes pointing forward and two back. Relatively short legs mean it can anchor itself securely. And the spiky central feathers in its long, stiff tail dig into the bark, bracing the bird against the tree while climbing. So when traveling upward, the woodpecker’s a master. Hitching down? Not so much—usually they’ll fly.

Nuthatches are also expert climbers, but they can easily go up and down. A nuthatch’s tail is shorter than a woodpecker’s, but its legs are longer and very strong. It walks over the bark by grasping it with one leg while using the other for a prop. And it has a rear-facing toe equipped with a long, sharp claw that’s ideal for hanging on while heading downward