Drongo

An enterprising bird, the drongo forages individually
on the insects herded out by the movements of other
flocking birds. Insects compose 100 percent of a
drongo's diet. As one might expect, drongos that tend to associate with
larger flocks of other bird species (more than 20 birds) show increased
numbers of foraging trips and harvest a larger number of insects in a
given time than those associated with smaller flocks. The drongo and
the other bird species do not compete for the same food source, so the
relationship -- known as a commensal relationship -- is a good one for
the drongo. Drongos are considered remarkable for the courage with
which they will attack and dive off larger birds.