PHYSIOLOGICAL-CHARACTERISTICS OF ARCTIC TERN STERNA-PARADISAEA CHICKSIN RELATION TO EGG VOLUME

The effect of egg volume on body mass, body composition and growth rat e in arctic tern Sterna paradisaea chicks was studied at Ny-Alesund, o n Svalbard (78 degrees 55'N, 12 degrees 00'E), in order to investigate whether differences in egg size influence the physiological character istics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large e ggs had larger body masses than hatchlings from small eggs, with 71% o f the overall variation in body mass accounted for by egg volume. In n ewly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in propo rtion to egg volume. Hatchlings from large eggs, however, had dispropo rtionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, ind icating that the leg muscles of small hatchlings were functionally mor e mature. There was a weak, but significant, correlation between egg v olume 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 Arcti c tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During emb ryonic growth in small eggs, however, there seems to be a greater rela tive usage of yolk, resulting in a more developed leg musculature. Thi s may partly compensate for the higher mass-specific heat loss in smal l hatchlings.