It is absurd to speak of a bird that behaves in this manner as being defeated in battle. It does not suffer defeat. It merely declines to give battle.
The general rule in nature is, “Never fight when a fight can be avoided.”
This rule is unconsciously followed by all birds, except those that have nests.
The most familiar example of the rule in operation is the well-known habit of birds of surrendering their perches to new-comers. When individual A flies to a perch occupied by individual B the latter almost invariably gives way without demur. The particular perch is of no value to the occupier, but a whole body may be a matter of life or death.
Biological science is at present in a rather peculiar position. Biologists are divided into two parties. On the one side stand the theorists and their followers; on the other the practical men who think for themselves. At present, the theorists are the party in power (and they are quite Lloyd-Georgian in their methods), while the practical men, the breeders and the field naturalists, form the opposition. The reason of the division is that many facts, that have come to light lately, do not fit in with the theories that hold the field.
Now, when facts are discovered which militate against a theory the proper course for the holder of the theory is to test carefully the alleged facts, and if they prove to be really facts to discard or modify his theory.
Unfortunately the professional biologists of to-day do not usually follow this course. They have made fetishes of their theories, which they worship as the Israelites worshipped the golden calf. The consequence is that they feel in honour bound either to ignore or to gloss over the facts that are subversive of their fetishes. When they write books in honour of their fetishes, they omit many facts which tend to show that their fetishes are shams. They regard the discussers of the awkward facts as enemies to be crushed. Hence the gulf between the two classes of biologists.
One of the fetishes of the present day is the theory of protective mimicry. Butterflies and moths are the organisms which exemplify best this theory.
It often happens that two species of butterfly occur in the same locality which resemble one another in outward appearance. In such cases zoologists assert that one species mimics the other. They maintain that this mimicry has been brought about by natural selection, because the one species profits by aping its neighbour. The species that is copied is said to be unpalatable. The copy-cat, if I may use the expression, may be either palatable or unpalatable. In either case it is believed to profit by the resemblance. If it is edible the birds that are supposed to prey upon butterflies are said to leave it alone, because they mistake it for its unpalatable neighbour. This resemblance of an edible form to an unpalatable one is called Batesian mimicry.