Which unusual item have at least four penguin species been observed eating, possibly to acquire collagen?

Answer

Jellyfish

Species like Magellanic and Adélie penguins have been observed eating jellyfish, despite the low caloric content. Scientists hypothesize this might be an attempt to acquire specific micronutrients like collagen.

Which unusual item have at least four penguin species been observed eating, possibly to acquire collagen?
fooddietpenguin