Amino Acid Composition of Feather Barbs and Rachises in Three Species of Pygoscelid Penguins: Nutritional Implications

To evaluate the nutritional challenge faced by molting penguins we studied the composition of contour feathers of three species of penguins, Pygoscelis adeliae, P. antarctica, and P. papua. The feathers of these species are nearly identical in structure and chemical composition. They have a unique broad, flat rachis that accounts for 60 to 70% of the total feather mass. Their barbules are pennaceous and able to interlock tightly, which probably accounts for the shedding of plumage in sheets rather than as individual feathers. Compositionally, the penguin feathers are remarkably similar to feathers of other species of birds representing six different orders and varied life-styles. Whole penguin feathers averaged 8-10% water. Ash contents of P. adeliae and P. antarctica feathers averaged less than 1%, but P. papua averaged 2.6%. The nitrogen contents of the barbs were nearly identical in the three species and averaged 16.4%. The nitrogen content of the rachises of P. adeliae and P. antarctica feathers averaged 16.4%, but was slightly less in P. papua (15.5%), probably due to the higher ash content and slightly higher pigment content in this species. The most abundant amino acids in barbs and rachises were gly, pro, ser, cys/2, val, and leu. Six nonessential amino acids (ala, asp, glu, gly, pro, ser) made up 52.5 and 54.3% of the barbs and rachises, respectively. The basic amino acids (lys, his, arg) were among the least concentrated amino acids. This amino acid profile is typical of mixed feather keratins. The high cys/2 contents of feather proteins results in a large mismatch between nonkeratinous mixed tissue proteins and feathers that could result in highly inefficient reutilization of tissue amino acids in feather synthesis during the molt fast. Some compensatory mechanisms that penguins might use to minimize this inefficiency are discussed.