These yellow-billed oxpeckers (Buphagus africanus) are feeding on small insects and parasites on the face of this Cape buffalo in Maasai Mara National Park, Kenya. Oxpeckers graze exclusively on the bodies of large mammals. Oxpeckers were previously thought to have a mutualistic relationship with the large mammals on which they graze. However, recent reseasrch suggests that oxpeckers may be parasitic, as they have been observed opening new wounds to drink blood.
It is unclear from this video whether they are eating parasites, or if they are enjoying the nasal, ear, and eye secretions of its perch. Although the feeding appears vigorous, the Cape buffalo seems to tolerate them, suggesting some degree of benefit to the mammal.