Symbiosis is an interesting word meaning ‘living together’ which derives from the Greek syn = together and biono = living. It is frequently used in the form of symbiotic relationships between plants / animals / birds. A very common example of a symbiotic relationship between birds and animals is the presence of Cattle Egrets that follow close in the wake of grazing cattle.
They are also often seen in the company of buffalo or zebra.
What these birds are doing is catching insects that are disturbed by the movements of the grazing animals. This is a type of commensalism whereby the birds benefit enormously from the animals, although what the latter get out of the relationship is uncertain – unless the birds act as a warning system perhaps.
I suspect this Red-winged Starling was using the bull as a convenient perch for the same reason – there were several other cattle grazing nearby.
A symbiotic relationship with more mutual benefit would be this one between the Red-billed Oxpeckers and the Nyala bull: the oxpeckers probe the skin and ears of animals in order to feed on the parasites harboured there. This benefits both them and the animal concerned.
In the case of these oxpeckers on a Cape buffalo, only one appears to be ‘working’, while the others are enjoying a free ride!