Red-billed and yellow-billed oxpeckers are two African bird species that live almost entirely on the backs of large mammals. Both are about 20 cm (7.9 in) long, plain brown with buff underparts, and strong feet for clinging to hides.

The most obvious distinction is in the bill: the red-billed is bright red, while the yellow-billed is yellow at the base and red at the tip. Rump color also separates them. Yellow-billed oxpeckers show a pale buff rump, while red-billed oxpeckers have a dark rump that blends with the back. Juveniles of both are duller with brown bills that shift to adult colors. Adults weigh 42-59 g (red-billed) and 57-71 g (yellow-billed).

Oxpeckers are restricted to sub-Saharan Africa. Yellow-billed birds dominate in West and Central Africa, from Senegal to Sudan, while red-billed oxpeckers are more common in East and Southern Africa, from Sudan south through Kenya, Tanzania, Zambia, and Zimbabwe into northern South Africa.

Where their ranges overlap, red-billed oxpeckers usually outnumber the yellow-billed. Both thrive in grasslands and lightly wooded savannas, often near water. They ride livestock such as cattle and goats, as well as wild species including Cape buffalo, wildebeest, giraffes, hippos, rhinos, and impalas.

Oxpeckers are obligate ectoparasite feeders that specialize in ticks and other parasites. An adult can remove more than 100 engorged ticks or several thousand larvae in a single day. Yellow-billed oxpeckers often tackle large Amblyomma ticks on cattle and buffalo, while red-billed birds focus on smaller Boophilus ticks across a wider range of hosts. They also consume skin flakes and insects found on mammals.

Blood is also part of their diet. Both species peck at wounds, drink from them, and may keep sores open by removing scabs. This dual role has fueled debate over whether oxpeckers are parasites or partners.

On the one hand, they remove parasites and can serve as early warning systems. On the other hand, their blood-feeding can delay healing. Modern research suggests the balance is mostly mutualistic.

Rhinos with oxpeckers on their backs, for instance, detect approaching humans far more reliably than rhinos without them. This earned the birds the nickname “the rhino’s guard.”

Oxpeckers are flocking birds that often gather in chattering groups on the backs of herds. Their calls are sharp hisses or crackles, slightly different between species, and double as alarms to their hosts. They sometimes roost directly on mammals at night, especially buffalo, using them as safe perches. Young birds beg with chirps until adults feed them.

Oxpeckers nest in cavities in trees or termite mounds, lining them with animal hair. Red-billed oxpeckers usually lay 2 to 5 eggs, while yellow-billed oxpeckers lay 2 to 3. Both parents incubate for about 12 days, and chicks fledge in 4 to 5 weeks. Cooperative breeding is common, with older offspring helping raise the next brood.

Courtship sometimes happens right on a mammal host, and fledglings quickly learn to forage by riding along with adults. In favorable seasons, pairs may raise two or three broods. Their dependence on cavities means that the loss of old trees can limit nesting opportunities.

Oxpeckers are highly specialized mutualists unique to Africa. By consuming ticks, they improve host health and reduce disease risk. Several birds may work over a single buffalo or rhino, methodically picking through fur. Alarm calls add another layer of vigilance for the herd. Though their blood-feeding can prolong wounds, the overall effect appears more beneficial than harmful.

Beyond bill color, red-billed oxpeckers have a yellow eye-ring around red eyes, while yellow-billed oxpeckers lack it. Red-billed birds often perch high on hosts, such as giraffe rumps, while yellow-billed may stay lower on the body. Both sexes look alike.

Specialized claws, stiff tail feathers, and brush-tipped tongues let them cling, balance, and feed with ease. Their digestive systems are built to process tough tick chitin. Without access to their mammal hosts, they rarely survive long because their dependence is absolute.