hippos are a bit aggressive about space in the wild, but in most cases herds of various animals tend to play keep away from one another and only form a herd of mixed species if there is something to gain from another, but no one but fish really gain from a hippo. most of the pictures ive seen from this zoo of activity like this just appears to be just play sparing. I am pretty sure that is a juvenile hippo, though i've been wrong before, this could just be a couple of males without other males of their own species and age to spar with.
There was also a notorious hippo "Hercules" at Belle Vue Zoo (Manchester) in the 1960s that killed and ate a Malayan tapir, a pygmy hippo, some flamingos and various other birds.
