The bird on the hindmost Eland is a Red-billed Oxpecker (uniformly red bill & uniform upperparts)which is said to be much commoner than the Yellow-billed Oxpeckers apparent on the middle Eland. We saw far more Yellow-billed Oxpeckers than red-billed. Yellow-billed Oxpeckers are larger with a predominantly yellow bill which shows up well at a distance as does the paler rump which contrasts with the darker upperparts.