How can you tell the difference between a male and female penguin?

Question

How can you tell the difference between a male and female penguin?

Answer 1

the guys wear bow ties.

Answer 2

If you're a penguin, you know.   :)

Answer 3

Behavior... there are no distinguishing features.

Answer 4

The female penguin makes the most noise.

Answer 5

the pedicure

Answer 6

Not just by looking, certainly. You could always pay attention to their habits -- females go out to sea at a certain time and males sit on the egg, then it reverses. The schedule is consistent and useful, but determining gender this way would take a long time.

I believe there is a technique for it, but I am unsure of what it may be, aside from DNA testing.