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The lives of oxpeckers are so linked to those of large, hoofed game
or domestic cattle that in West Africa where game is scarce the birds
depend on cattle, and their range is restricted accordingly. There the
cattle are confined to the higher and more northern areas, free of
tsetse flies, from Senegal to Northern Cameroon. Thus tsetse flies help
to determine the limits of the oxpeckers' range.
Except for their nesting, which is in holes in trees, and their
sleeping, most of their time is spent on the bodies of the larger
herbivores. There they run about over the hides and legs of the beasts,
like woodpeckers on a tree. They stay remarkably close to the animals,
and even ride on them as they travel. The oxpeckers' food is largely
ticks, which it gets from the hide of the animal by working over it
with the side of its bill, shearing off the ticks with a scissorlike
action of its mandibles. But when an animal has sores or cuts or
scratches the oxpecker may peck into them, and eat flesh and blood of
its host.
Correlated with this unusual and close relationship, a modification
in the oxpeckers has taken place. There are only two species, both
African, and they are dull-colored, modified starlings. The legs are
stout, with curved, very sharp claws for clinging to the hides of
animals, and the bill, very sharp at the tip, with the cutting edge of
the mandible very sharp to aid in scissoring off ticks.
All the larger herbivores are attended by oxpeckers except the elephant
and the hippo, but the favorite seems to be the rhino, and for this
he's sometimes called the rhino bird as well as tickbird and oxpecker.
The rhino gives the bird its food, and in return the bird provides a
service of a value difficult to evaluate. It acts as a sentinel and
may warn the rhino of the approach of hunters, for which habit it is
execrated by sportsmen.
It would seem that such relationships could have developed only where
the supply of big game was large. With the introduction of cattle
and other domestic animals it was natural the oxpecker should turn
its attention to them. Here the question arose as to the attentions
of the oxpeckers being harmful or otherwise to the herds. Mr. R. E.
Moreau, formerly of the East African Research Station at Amani, has
investigated the problem. He finds that white men who own herds tend
to consider the oxpecker a nuisance; Africans tend to consider it
beneficial and some African cattle owners object to having the birds
killed; the beasts themselves tolerate the birds.
There is the possibility on the one hand of oxpeckers spreading certain
cattle diseases that are mechanically transmitted, and on the other
hand they may help reduce disease by eating ticks, the vectors of
certain diseases. Of course dipping the cattle takes care of ticks on
them, and here we see another indirect effect of civilization on bird
life. When cattle have been dipped the oxpeckers disappear from the
herd. Perhaps it is because there is no longer food for them there;
perhaps they get enough of the poison dip left on the beasts' hair to
be lethal.