Physiological characteristics of Arctic tern Sterna paradisaea chicks in relation to egg volume
AbstractThe effect of egg volume on body mass, body composition and growth rate in Arctic tern Sterna paradisaea chicks was studied at Ny-Ålesund, on Svalbard (78°55'N, 12°00'E), in order to investigate whether differences in egg size influence the physiological characteristics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large eggs had larger body masses than hatchlings from small eggs, with 71% of the overall variation in body mass accounted for egg volume. In newly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in proportion to egg volume. Hatchlings from large eggs, however, had disproportionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, indicating that the leg muscles of small hatchlings were functionally more mature. There was a weak, but significant, correlation between egg volume and growth rate. However, a residual analysis made to eliminate the effect of egg volume showed no correlation between hatchling body mass and growth rate. The results of the present study show that Arctic tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During embryonic growth in small eggs, however, there seems to be a greater relative usage of yolk, resulting in a more developed leg musculature. This may partly compensate for the higher mass-specific heat loss in small hatchlings.
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