Since 1968 I have had varying degrees of responsibility for a variety of Penguins. Birds have disappeared, not many I'll grant you, but a few have gone without a trace. A fox has nearly always been the suspected culprit.
Chicks have gone too. Much easier to explain. A rat, a crow, a seagull, a stoat....but a cannibal penguin?
I'd be lying if I said the thought has not passed fleetingly through my head, but I never entertained the idea seriously. I never met anyone who suggested this was a real possibility. I have never read of it happening either in the wild or in captivity.
Here though we have video footage of this actually taking place. How common it is we probably will never know without extensive research.