How many penguins die during migration?

Question

I remember from March of the Penguins that a certain amount of Penguins go out to migrate a much smaller number actually end up returning.. does any one know that number?

Answer 1

i forgot to ask them... d**n it!

Answer 2

I would think at least 50% because that would be an optimal number for population control. The percentage could be higher. Again, I am just speculating.