[fnovd]

This is a hierarchy of one stratum (birds) cooperating to dominate another stratum (fish).

If anything, this link shows that operating effectively within a hierarchy has clear advantages to survival.

[bwestergard]

The question was whether there were animal species that do not have internal hierarchies. I gave an example.

I don't myself believe that the question is relevant to social relations among homo sapiens, but it's better that people be aware of the variety of animal behavior.