The answer would be gas I believe
Male Birds are usually the colorful birds to attract mates while females are camouflaged to protect their eggs/hatchlings. Ground birds need to be camouflaged because they are easy prey and they have their nests on the ground.
Polypeptide chains undergo some modifications before they become fully functional. Some of these modifications include: proteolytic cleavage, lipidation and glycosylation. Proteolytic cleavage refers to the removal of some amino acids from a polypeptide chain by proteases in order for the protein to become active. An example of a substance that is modified through this process is insulin.