low trees and
boxes, as the woodpeckers and wagtails. Thus the English starling will
occasionally impose upon and dispossess the green woodpecker. In the
process of nature in such cases the stronger of the two birds would
retain the nest, and thus assume the duties of foster-parent. Starting
from this reasonable premise concerning the prehistoric cuckoo, it is
not difficult to see how natural selection, working through ages of
evolution by heredity, might have developed the habitual resignation of
the evicted bird, perhaps to the ultimate entire abandonment of the
function of incubation. Inasmuch as "we have no experience in the
creation of worlds," we can only presume.

Indeed, the similarities and contrasts afforded by a comparison of the
habits of all these birds--European cuckoo, American cuckoo, and
cow-bird--afford an interesting theme for the student of evolution. What
is to be the ultimate outcome of it all? for the murderous cuckoo must
be considered merely as an innocent factor in the great scheme of
Nature's equilibrium, in which the devourer and the parasite would seem
to play the all-important parts, the present example being especially
emphasized because of its conspicuousness and its violence to purely
human sentiment. The parasite would often seem to hold the balance of
power.

[Illustration]

Jonathan Swift's epitome of the subject, if not specifically true, is at
least correct in its general application:

"A flea
Has smaller fleas that on him prey;
And these have smaller still to bite 'em;
And so proceed _ad infinitum_."

Even the tiny egg of a butterfly has its ichneumon parasite, a
microscopic wasp, which lays its own egg within the larger one, which
ultimately hatches a wasp instead of the baby caterpillar.

But who ever heard of anything but good luck falling to the lot of
cow-bird or cuckoo, except as its blighting course is occasionally
arrested by the outraged human? They always find a feathered nest.

In this connection it is interesting to note certain developments in
bird life upon the lines of which evolution might work with
revolutionary effect. Most of our birds are helpless and generally
resigned victims to the cow-bird, but there are indications of
occasional effective protest among them. Thus the little Maryland
yellow-throat, according to various authorities, often ousts the
intruded egg, and its broken remains are also occasionally seen on the
ground