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This paper deals with late embryonic and postembryonic weight changes in the yolk sac and liver of mallard ducklings (Anas platyrhynchos) from Slimbridge, England. The amount of yolk which remained after hatching was thought to depend in part on heredity and in part on the speed of the hatching process. Yolk was mostly used up during hatching and in the first day of life and was, therefore, an unimportant food store after ducklings left the nest. During the second day the yolk sac decreased at much the same rate in fed and unfed birds, indicating that its shrinkage does not depend on the bird's nutritional state. Birds without food for the first 48 hours were in good condition and apparently existed mainly on their body fat reserves. Liver weight increased as yolk decreased before and immediately after hatching, although the birds did not feed. At 2 weeks, this organ was relatively enormous, and some proportional decrease must occur as the mallard matures.
The Journal of Wildlife Management © 1965 Wiley