Composition of Eggs of Several Bird Species

--This paper presents the lipid, nonlipid dry matter, and water contents of the eggs of the Starling, Coturnix Quail, Mourning Dove, Laughing Gull, and Mallard and compares the data with published accounts of the eggs of other species. The lipid level of the yolk and the percentage of yolk in the egg increase in direct relation to the precocity of the young at hatching. The high lil•id content of the eggs of precocial species is related primarily to their long incubation periods, resulting in a larger total metabolic requirement than for the embryos of altricial species. The high water levels of the eggs of altricial species are a direct consequence of the high water levels of the chicks at hatching.---Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19174. Accepted 19 November 1975. THE proportions of yolk, white, and shell in the eggs of birds varies greatly between species (Meyer 1930, Asmundson et al. 1943, Romanoff and Romanoff 1949). The eggs of species with precocial development, particularly waterfowl, have large yolks (about 35% egg weight) compared to the eggs of birds with altricial development (about 20% egg weight). Nice (1962) found a close correspondence between yolk size, expressed as a percent of egg weight, and her categories of development types. At one extreme, the eggs of Megapodius have very large yolks (62%) and young Megapodius are completely independent of parental care after hatching. At the other extreme, eggs of altricial passerines contain 15 to 27% yolk. Collins and LeCroy (1972) used the ratio of yolk to albumen in the egg as an index to the degree of precocity of development. This index was found to average 0.64 for precocial species, 0.28 for altricial species, and 0.49 for two species of terns with semialtrical (intermediate) development. Because yolk is more dense than albumen and contains 20-40% lipid, the chemical energy of the contents of fresh eggs varies directly with yolk size. Caloric equivalents of egg contents, summarized by King (1973) from numerous literature sources, were on average about 1.05 kcal/g for altrical species, 1.6 kcal/g for galliform species, and 1.8 kcal/g for anseriform species. These figures were obtained primarily by bomb calorimetry of whole eggs, although energy contents have also been calculated from Romanoff and Romanoff,s (1949) chemical analysis of the eggs of many precocial species. Lawrence and Schreiber (1974) and Schreiber and Lawrence (1976) have emphasized that it is more important to determine the chemical constituents of eggs than to calculate the proportions of yolk and albumen or to measure caloric values directly. As proportions of lipid, protein, and water in the yolk vary between species, one cannot reconstruct the chemical composition of an egg solely from the proportions of albumen and yolk, together with the chemical composition of the albumen and yolk in eggs of domesticated precocial species. In addition, caloric values cannot be used to calculate the proportions of lipid, protein, and water in the egg. Schreiber and Lawrence (1976) also point out that neither the Brown Pelican (Pelecanus occidentalis) nor the Laughing Gull (Larus atricilla) fits particularly well into categories of development pattern based on percent yolk or the yolk/albumen ratio. As a greater variety of species are examined, more exceptions undoubtedly will be found and classifications of development pattern or the relationship of egg contents to development pattern will have to be modified accordingly. This paper presents the lipid, protein, and water contents of the eggs of the 350 The Auk 94: 350-356. April 1977 April 1977] Bird Egg Compositions