iBT TOEFL Topic Vocabulary Breakthrough Unit 075

iBT TOEFL Topic Vocabulary Breakthrough Unit 075
Author: Li Xiaolai

75. The main component of feathers is keratin, a flexible protein that also forms the hair and fingernails of mammals. Feathers provide the strong yet lightweight surface area needed for powered, aerodynamic flight. They also serve as insulation, trapping pockets of air to help birds conserve their body heat. The varied patterns, colors, textures, and shapes of feathers help birds to signal their age, sex, social status, and species identity to one another. Some birds have plumage that blends in with their surroundings to provide camouflage, helping these birds escape notice by their predators. Birds use their beaks to preen their feathers, often making use of oil from a gland at the base of their tails. Preening removes dirt and parasites and keeps feathers waterproof and supple. Because feathers are nonliving structures that cannot repair themselves when worn or broken, they must be renewed periodically. Most adult birds molt — lose and replace their feathers — at least once a year.

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