The tickbird and the giraffe have a symbiotic relationship that some scientists describe as mutualism and some as parasitism. This interspecies partnership is in favour of the giraffe because he can live without the tickbird, while the tickbird is dependent on the giraffe for much of his food.
A close ecological relationship involving two or more species can benefit all parties (mutualism) or none (competition). It can also benefit one party without affecting the others (commensalism) or help one while harming the others (parasitism).
The relationship between the giraffe and the tickbird hovers somewhere between mutualism and parasitism because the tickbird seems to derive greater benefit from the relationship than the giraffe.
Tickbirds (red-billed and yellow-billed oxpeckers) have long been thought to remove ticks from their hosts, to the benefit of both — the bird eats the ticks, and the host is relieved of blood-sucking, disease-carrying parasites.
A secondary benefit to a host from the tickbird's presence is a sort of early warning system, since the birds make a hissing sound if they sight an enemy.
This is of less benefit to the giraffe than to other hosts because the giraffe has the advantage of great height and keen eyesight and is fully capable of spotting predators without the bird's assistance.
Another example of mutualism is the relationship between crocodiles and Egyptian plovers. The crocodile leaves its mouth open while basking on the shore, and the bird walks in and picks bits of rotting flesh from between the croc's teeth. The plover gets food and the croc gets a cleaner mouth. The determining factor of mutualism is consent: the crocodile does not have to open its mouth for the bird.
So next time you are in the park, be on the lookout for species that have symbiotic relationships.