Egg Formation in Fiordland Crested Penguins (Eudyptes pachyrhynchus)

Female Fiordland Crested Penguins (Eudyptes pachyrhynchus) lay a clutch of two eggs, the second being significantly larger than the first. To investigate this disparity, I gave experimental birds a single oral dose of 300 mg Sudan black B dye. This was deposited in their yolks over a period of several days, and helped to reveal the timing of egg formation events. The yolks were pale yellow and lacked marked structure except for the dye band. Staining the yolks with dichromate revealed faint daily rings. For both first and second eggs, mean time for yolk formation was 16 days (range: 14-18 days). The larger, second eggs contained higher proportions of albumen and lower proportions of yolk than first eggs; shell proportions were constant. During the female's fasting period of egg formation, the amount of nutrients transferred from tissues to eggs was not large compared with body reserves. The mean interval between date of yolk completion and laying was seven days (range: four to nine days). The relative positions of the dye bands showed that the first yolk grew for several days before the second yolk began to grow.