Oxpeckers, often called “tick birds,” are two species of small birds native to the savannas and bushveld of Sub-Saharan Africa. The two species, the Red-billed Oxpecker (Buphagus erythrorhynchus) and the Yellow-billed Oxpecker (Buphagus africanus), are known for their habit of perching on large mammals like rhinoceroses, giraffes, and cattle. This behavior has given them their common name. These birds spend the majority of their daylight hours on their massive hosts, forming one of the most visible interspecies relationships in the ecosystem.
Primary Foraging and Diet
The primary activity of the oxpecker is foraging on the bodies of large mammals, and their anatomy is adapted for this task. They possess strong, scissor-like claws that allow them to grip the hide tightly and maintain their position on a moving host. Their stiff, wedge-shaped tail feathers also act like a prop, helping them to brace themselves vertically against the animal’s skin while they feed.
Their diet centers on ectoparasites, such as ticks, lice, and fleas. A single oxpecker can consume over 100 blood-engorged ticks in a day, or more than 12,000 tick larvae. They use a feeding technique called “scissoring,” where they rapidly open and close their stocky beaks while running them through the animal’s fur to locate parasites. Beyond parasites, they also consume other material found on the host’s skin, including dead skin flakes, dandruff, and mucus.
The Ecological Debate on Host Interaction
The relationship between the oxpecker and its host has long been considered a textbook example of mutualism, where both species benefit. The host animal is relieved of potentially harmful parasites, and the oxpecker receives a steady food source. However, scientific observation has revealed a more complex interaction that challenges this simple mutualistic label.
A significant point of controversy is the bird’s tendency to consume the host’s blood, a behavior known as hematophagy. Oxpeckers will peck at existing wounds, often preventing them from healing by actively enlarging them to keep the blood flowing. This behavior is particularly prevalent when the preferred food source of ticks is scarce, suggesting that the birds exploit their hosts when necessary.
This wound-feeding behavior means the relationship can shift toward facultative parasitism, where the oxpecker benefits at the host’s expense. Some studies have indicated that the cost of blood loss and delayed wound healing for the host may outweigh the benefit of tick removal. The birds are also known to selectively target ticks that are already engorged with blood. The outcome of the relationship is context-dependent, moving along a continuum between mutualism and parasitism based on the availability of ectoparasites.
Secondary Functions and Communication
The oxpecker acts as a crucial sentinel for its host, distinct from its role as a cleaner or a parasite. They emit loud, sharp alarm calls when they detect an approaching threat, such as a human or a large predator. This warning system is particularly beneficial to species with poor eyesight, such as the black rhinoceros.
Rhinos accompanied by oxpeckers are significantly more likely to detect a human approach, and they detect them at much greater distances than those without the birds. The warning call often prompts the rhino to re-orient itself, facing the direction of the threat. This sentinel function, which has earned the Red-billed Oxpecker the Swahili name Askari wa kifaru or “the rhino’s guard,” may be the most consistently beneficial service the bird offers its host.
Oxpeckers also engage in specialized feeding behaviors. They have been observed feeding on earwax, which is thought to contain bacteria that aid their digestion. They will also ingest mucus from around the host’s eyes and nose, showcasing their thorough approach to gleaning various secretions and materials from the animal’s hide.