The relationship between oxpeckers and African ungulates has traditionally been
considered mutualistic, because the birds were thought to reduce the tick loads of their hosts. However, recent field studies have questioned the validity of this
assumption. Red-billed oxpeckers were found to have no impact on the number of ticks living on domestic cattle and they also prolonged the healing time of wounds (Weeks  Anim Behav 58:1253–9; Weeks  Behav Ecol 11: 154–60). One of the important limitations of these studies is the fact that the two species did not coevolve, and therefore the results may not be representative of the relationships between oxpeckers and their native African ungulate hosts in general. We carried out observations between red-billed oxpeckers and one of their natural host species, the black rhino, in captivity, to investigate their relationship. We found that the rhinos had oxpeckers present on them for almost half (approximately 45%) the time that the two species were in the same enclosure. The oxpeckers spent a large proportion (approximately 40%) of their time on the rhinos foraging, and mostly at wounds. We observed oxpeckers opening wounds on their hosts for the first time; they created four new wounds on the female rhino and nine on the male. Although the rhinos were intolerant of the presence of the oxpeckers at wounds, only approximately 43% of their attempts at removal were successful. Therefore if oxpeckers are housed with any of their native hosts in captivity, observations should be carried out to determine the activities of the oxpeckers on those hosts. Zoo Biol 23:347–354, 2004.