Amino Acid Composition of the Plumage of the White-Crowned Sparrow

Abstract

To provide baseline data for estimating the dietary amino acid requirements of molting birds, we measured the amino acid composition, nitrogen and sulfur content, and heat of combustion of the homogenized plumage of six White-crowned Sparrows (Zonotrichia leucophrys gambelil). On the average, the plumage contained 15.22% nitrogen, 3.14% sulfur, and 0.86% ash. Of the 17 amino acids measured, serine, proline, cystine/2, and glycine (in that order) were most abundant, comprising 46 mol% of the hydrolysate. Nonessential amino acids predominated (68 mol%). Cystine/2 contributed 11 mol%. Variation of amino acid composition among the plumages of the six birds was small (coefficient of variation = 2-7%). The heat of combustion of the homogenized plumages was 21.69 kJ/g of dry mass. Although exact quantitative comparisons are not possible, the amino acid composition of White-crowned Sparrow plumage in general parallels that of other species. Its cystine/2 and sulfur content, however, are noticeably greater than that reported for any other species thus far examined (primarily pale and domesticated). The quantities of exogenous nutrients required per unit time in the production of eggs, feathers, or tissues can be estimated from a knowledge of the growth rates and composition of the synthesized products. If either the ratio of calories to specific nutrients is low or the concentrations of dietary nutrients are much less than their concentrations in products, then an animal engaged in production must (1) eat in excess of caloric requirements in order to obtain adequate materials, (2) rely on endogenous materials, if available, or (3) alter the rate, timing, or pattern of production so that requirements match nutrient availability. Depending on circumstances, any or all of these adjustments might be invoked. In the case of avian molt, it has been noted that the amino acid cystine is much more concentrated in feathers than in the foods that many birds consume (Hanson 1962, Newton 1968, Gavrilov and Dolnik 1974). This has fostered hypotheses that attempt to relate energy requirements, feeding tactics, and alterations of body composition during molt to dietary cystine availability (Gavrilov and Dolnik 1974). The reliability of such hypotheses depends on accurate estimates of the cystine content of the entire plumage. Although this emphasis on cystine may be questionable, it is nevertheless necessary to know the amino acid composition of whole plumage before this or other hypotheses about amino acids as limiting factors during molt can be critically examined. Although there have been many analyses of the amino acid composition of single feathers, feather parts, and purified keratins (Block 1939, Ward and Lundgren 1954, Schroeder and Kay 1955, Harrap and Woods 1964, 1967, Kemp and Rogers 1972, O'Donnell and Inglis 1974, Busch and Brush 1979, Nitsan et al. 1981), none except the last has reported the average amino acid composition of an entire plumage. Also, nearly all of these analyses involved feathers from domesticated species of birds having white or near-white plumage. Because differences occur in the amino acid composition of feathers from different species as well as among feather parts from a single species (Schroeder and Kay 1955, Harrap and Woods 1964, 1967) extrapolations of percentage composition from purified keratins or feather parts to whole plumage or from one species to another might be tenuous. As we were reluctant, in nutritional investigations to be reported elsewhere, to depend on such extrapolations without testing their reliability, we undertook the following analysis. MATERIALS AND METHODS We sacrificed six White-crowned Sparrows (Zonotrichia leucophrys gambeli) captured during the autumn migration in eastern Washington and plucked all the feathers from them. We put the feathers from each bird into a loosely woven cloth bag and washed them according to the methods of Harrap and Woods (1964). We then macerated the air-dried feathers with shears until they formed a felt-like,