Penguin parenting

You know how they say that penguins can recognize their babies' calls? How, in an ice field full of hundreds upon hundreds of penguins, mother and baby miraculously find each other by voice alone?

John and I have been wondering something. Do the penguins actually have the auditory acuity to distinguish each other's voices? Or is this all just a by-product of their well-known devotion to the community above all individual interests?

Think about it. In Antarctica, no penguin can survive alone. Cooperation is vital, even if it means putting aside one's own interests for the moment. When penguins huddle together to keep warm, each one takes its turn on the outside of the huddle to keep others warm, as well as taking its turn at the middle to warm itself. If a penguin community ever had a large number of individuals that were, well, individualistic, that community and its gene pool would die.

And it's documented that mother penguins whose babies have died will actually fight over a baby to adopt. They have no problem with raising babies that aren't their own.

So the question John and I are asking is, has anyone actually done a tagging or gene-testing study to determine that the penguins do find their own babies? Or is it possible that they just call out and adopt the first baby that answers?

I mean, that way, pretty much every baby gets a mother, and it happens faster than it would if they took the time to seek out their own young. From the point of view of the community, which is what matters for penguins, it would make sense.

I'm really curious. Any thoughts?