Movement costs energy, which arctic birds might better spend keeping themselves warm. Birds in cold environments are therefore very careful not to waste energy on unnecessary movements. When not actively hunting, many arctic birds – especially gulls and shorebirds – stand perfectly still for long periods of time to save energy. Shorebirds often crouch down low, with their feathers covering most of their legs and feet, a position that reduces the amount of the body that is exposed to the wind. Other birds stand on one leg, holding the other up against the body for warmth, or hide their head under a wing to keep it warm.