Enid Kitto, of Mornington, asks :-

Why are the eyes of the yellow-eyed penguin yellow?

Gordon Sanderson, an opthalmologist at Otago University's Medical School, responded.

The yellow-eyed penguin (Hoiho) is a rare penguin found mainly in Otago. It has distinctive yellow eyes and a band of yellow feathers stretching from the base of its bill past its eyes and over the back of its head.

How the eyes come to be coloured yellow is a relatively easy question to answer. The flat circular part of your eye underneath your cornea is called the iris, it makes the pupil bigger or smaller letting in more or less light. Eye colour comes from the iris. It gets its colour from a pigment called melanin. If you have a lot of melanin in your iris your eyes look brown, if you have none your eyes look blue. If you only have a little bit then your eye looks a sort of brownish yellow colour. The chicks of the yellow-eyed penguin are born with blue eyes. It is only when they grow up that their eyes change to yellow. Some babies are born with blue eyes and as they get older their eyes become brown.

The hardest question to answer is why these penguins have yellow eyes. Maybe it is so they can recognize their friends and family. This is called species recognition. Maybe it is so that fish called yellow-eyed mullet will not be afraid of them when they see their yellow eyes and the penguins can catch them.

One thing is certain, with blue and yellow eyes the Hoiho must continue to live in Otago.