228 
FRANCIS H. HERRICK 
The door is thus opened wide to parasitism in its initial stage, 
whenever the acceleration of egg-laying or the retardation of the 
building instinct becomes common, with or without irregularity 
in the egg-laying intervals. A later stage in the retrograde direc- 
tion is seen in the present-day habits of the common Argentine 
cowbird referred to above, which will lay in any kind of a nest, 
wastes its eggs, and though sometimes attempting to build 
is never known to rear its young. The visual stimulus produced 
by a nest seems to act mechanically upon this bird, much as the 
sight of an egg, although it be an artificial one placed in her nest, 
affects the female noddy tern. Watson^^ found that by placing 
such an egg in the nest of a laying'' noddy, he could change its 
habits from those of a layer" into those of a sitter." The 
mere sight and touch of such an egg seemed immediately to evoke 
the guarding and fighting instincts while the behavior of a ''sitter " 
was reversed if her egg was removed. The production of a large 
number of eggs would seem to have saved this Argentine starling 
from utter extinction. The North American cowbirds without 
doubt, have passed along a similar path, and if they once squan- 
dered their eggs in the same fashion, this practice has been elimi- 
nated with the greater precision of their newly developed instincts. 
The cuckoo of Europe has retrograded into parasitism through 
a course essentially similar, by the diversion of some of its own 
instincts into slightly different channels, and by the acquisition 
of new ones in both adult and young. Thus we find this cuckoo 
today frequently dropping its eggs on the ground, and when it 
does not abandon them, carrying them in bill to the nest of a 
nurse. This, as already remarked, must be regarded as one of the 
most striking instinctive performances of this bird at the present 
time. Fortunately we can point to a quite similar act in the black- 
billed cuckoo of the New World, for, as we have seen, when this 
bird's nest is disturbed, it has been known to remove its eggs to 
another nest, and to continue to care for them. It seems very 
probable that this removal of the egg in bill, of which instances 
could be given in other species of birds, is the survival of a very 
primitive instinct, and is possibly related to the old instincts of 
Watson, John B. The behavior of noddy and sooty terns. Pub. 103, Carnegie 
Institution of Washington, p. 223. Washington, 1909. 
