The woodpeckers have strong sharp bills for digging insects out of wood and chiseling nest holes in trees. Most also use their bill to "drum" on resonant limbs, poles, tin roofs or drainpipes. This serves to warn rivals and establish territories. They have strong claws, short legs, and stiff tail feathers for climbing up tree trunks. Flight is usually undulating, with wings held against the body after each series of flaps. Males usually have some red on the head.