Influence of Age on Size of Eggs in Yellow‐eyed Penguins.

Summary. Between 1936–37 and 1953–54 inclusive, 892 eggs laid by Yellow‐eyed Penguins Megadyptes antipodes between the ages of 2 and 17 years, and 61 eggs of older birds, were studied in relation to age of female. The two eggs of the clutch of the Yellow‐eyed Penguin tend to be the same size, but they are statistically different in the five Eudyptes species for which data are available. The Yellow‐eyed Penguins may be divided into three groups according to age and size of eggs. (1) Immature penguins up to four to five years of age, (2) fully mature penguins from five years to around 13 or 14, and (3) aged penguins from 13 or 14 years to 19 + years, the oldest in my records. Two‐year‐olds produce significantly lighter and narrower eggs than older birds. Length is not significantly different but is very variable. Three‐year‐olds lay heavier and wider eggs than two‐year‐olds, but not so heavy nor so wide as four‐year‐olds. Penguins over 13 lay eggs that are lighter and more irregular in length, but some individuals still produce wide eggs. In the Royal Albatross Diomedea epomophora sanfordi age influences the size of the egg as it does in the Yellow‐eyed Penguin and some other birds.