Why is it that whenever there is a documentary with penguins in it, they always have to say how amazing it is that the mother penguins recognize their young? Would you recognize your own child in a crowd? If you had a stadium full of people or a crowded beach would you suddenly become confused and unable to recognize your own kids?
I think it is because we are primarily visual creatures, and we just can’t conceive of how the penguins can possibly recognize their chicks from all those chicks that look pretty much the same.
Penguins use auditory calls and cues to identify their chicks. How they can pick the individual voice of their own chick out of the cacophony of a colony is pretty amazing too.
ETA: It would be hard to pick out your child from 5,000 kids visually. It does become easier when using auditory cues. So the penguins have gotten that part right.