The buffalo, chewing the cud on the African savannah, is a walking menagerie. So, too, is the giraffe, and the elephant, and all the other large mammals on the grassland. What on first glance appears to be a single individual is just an illusion, for all of these animals are ecosystems in their own right. Nestled in the fur of the animal are small invertebrates: ticks, fleas and other blood-sucking parasites. These, in turn, are food for larger animals that make their home on the flanks of these megafauna.
The oxpecker is a small bird with a murky taxonomic history that spends almost all its time clinging to its mammalian host. It even courts and mates there. The only thing this bird can’t do is nest on its host – they do that in holes in trees – but it can still line these holes with hair plucked from its host’s body.
It seems apparent that the relationship between oxpecker and mammalian host started a long time ago, for the bird has evolved several adaptations to help it in this particular way of life. Its beak has become flattened so that it can put its head to one side and probe deep between the hairs of the coat that lie close to the skin, enabling it to find ticks and fleas to eat. Its tail, meanwhile, is stiff and short so that it can be used as a prop when the oxpecker climbs up the flank of a much larger animal.
The oxpecker gets all of its food from its mammalian host. At the same time, the large mammals seem to benefit by having their parasites removed and receiving regular cleans. A happy, healthy, two-sided relationship, right?
Er, not quite. There is a more sinister side to this bird. It has been discovered that although the oxpeckers eat ticks and other parasites, it seems that they might actually be after the blood of the mammalian host that is within the engorged tick rather than the tiny arachnid itself. If the oxpecker can access the blood directly, bypassing the tick entirely, then the bird will do so. If its host is injured, perhaps by a failed predator attack, the oxpecker may use its beak to scissor open the wounds and drink its blood. By keeping the wound open in this way, the bird gets a constant supply of blood but it also exposes its host to an increased risk of infection.
So are oxpeckers of any use whatsoever? Well, a study has shown that domestic cattle with oxpeckers on them seem to lose no more ticks than those that were bird-free, but their wounds took much longer to heal. Oxpeckers will even actively avoid ticks that haven’t recently fed because they have no blood inside them, leaving them to scurry around in the fur of their host. In fact, some animals such as elephants will even try to dislodge oxpeckers as soon as they land on them, perhaps realising that these birds are not as wholesome as they initially appear.