WATCHDOGS AT THE NEST [Ref]
A savage watchdog outside his master's house helps to protect it. If an intruder comes, the watchdog, if it's the right kind, simply bites him without preliminaries. There's a parallel to this in the bird world. Some birds often have their nests close to wasps' or bees' nests, or in trees inhabited by biting ants. The birds and the ants, wasps, or bees get along without disturbing each other. But when intruders come along the insects swarm out, biting or stinging and driving the intruder away. The insects are protecting their own homes, but one of the results, the protecting of the birds' homes, is just as satisfactory to the birds as if they did it on purpose. This building of birds' nests close to wasps' nests is a common practice with certain sunbirds and weaverbirds, especially in Africa. It occurs too often to be chance. The question naturally arises as to how much the birds understand of it all—do they actually seek out the association? That's difficult to say, but the facts of the association are still there.
Though some of these associations are evidently fairly common and chosen deliberately by the birds—and one can easily visualize how the protection works—field observations as to the natural enemies against which they are effective, and how effective they are, are largely lacking. Usually the records are something like those of Van Rossem for the Giraud's flycatcher in El Salvador, in which he points out that this bird usually nests in certain mimosa trees armed with numerous heavy, curved thorns. These thorns are hollowed out and inhabited by swarms of small but extremely hostile antlike insects, so that the nest is well protected. However, the effectiveness of ant and bee protection against human predation can be seen in the following.
Take the case of Mr. M. E. W. North, who arranged a rope to climb to a fish eagle's nest in East Africa. He had gotten about fifty feet up and was considering going out on the big limb on which the nest was, when he noticed a wild bee on his sleeve. Realizing that he was disturbing a wild-bee hive, and knowing that the sting of these vicious bees can be dangerous, fatalities having been reported, he came down his rope at express speed, crashing through projecting branches and brambles. Reaching the ground, he freed himself from the rope and fled to a safe distance, considering himself lucky to have received only three stings.
On another occasion, again in East Africa, Mrs. R. E. Moreau attempted to reach a hawk's nest to measure the eggs, but when she was up in the tree, savage, biting red ants drove her out.