Variation in the Composition of the Eggs and Chicks of American Coots

Abstract

I evaluated the composition of 97 fresh eggs and 43 one-day-old chicks of the American Coot (Fulica americana) to determine if the constituents of eggs or chicks show allometry. Heavier eggs contained proportionately less albumen but proportionately more yolk, and consequently had a higher energy density than lighter eggs. Albumen weight varied more among than within clutches, presumably due to variation in the qualities of coot territories during nesting. Within clutches, the lipid content of eggs declined with laying sequence, but albumen weights remained constant. Moreover, newly hatched chicks contained proportionately more lean dry material if they hatched from large eggs than if they hatched from small ones. These patterns of variation appear to increase the disparities in size of these asynchronously hatching young, and thus result in differential survival probabilities among siblings.