184 THE CONDOR Vol. XXHI 
action, is inexplicable in terms of the five senses, and must be based upon 
principles of which we have no definite knowledge. 
As a result of this conception, there has been a tendency to speculation 
rather than careful study, and certain of the phenomena of group behavior 
have been adduced as evidence in support of various mystical beliefs. 
An English writer who is presumably a very good naturalist has lately ad- 
voeated the opinion (Newland, 1917, p. 104) that every sentient being is an 
incarnate fragment of the All Mind; hence the members of a flock act in uni- 
son because they are directed by a common intelligence. Still more recently 
it has been insisted by Long (1919, p. 74 ff.) that a mysterious ‘‘natural tele- 
pathy”? is responsible for the passage of impulses from individual to individual 
in the animal flock. Dogs, wolves, caribou, Indians and Bushmen, he thinks, 
are possessed of a ‘‘supersense’’, an extremely useful appurtenance which 
civilized man has been careless enough to lose. Numerous other examples of 
more or less extravagant interpretations might be cited. 
Unfortunately for such views, the group-mind is not at all the perfect 
instrument that they assume. It often stumbles in a manner unworthy of an 
All Mind, and hesitates in a fashion inconsistent with the idea of a perfectly 
functioning natural telepathy. Furthermore, we are able to trace among gre- 
garious forms a progression from a simple to a complex type of organization ; 
in the case of the more loosely organized groups we are able to explain behay- 
ior in terms of known facts of psychology, and it is logical to suppose that 
greater complexity is a difference, not of kind, but of degree only. 
In a previous paper (Miller, 1921) attention has been called to the Bush- 
tit (Psaltriparus mimmus) as a bird manifesting a relatively simple and loose 
flock organization. Coordination here takes place as a rule rather slowly, and 
the observer is able to witness the actual steps in the process. 
When the Bush-tits behave at all as a unit, it is by the method that I have 
termed the ‘‘spread of impulse’’. If the flock moves from one place to an- 
other, it is because one bird, or occasionally two or three birds at a time, are 
stimulated by hunger to a change of location; the impulse spreads, not tele- 
pathically, but through the ordinary channels of sight and hearing, and the 
flock follows suit. If an enemy appears, it is sighted perhaps by only one 
or a few of the flock; from them the impulse spreads, almost instantaneously 
in this case, but through the medium of sound, to the others, so that those 
birds who may not have seen the enemy unite in the ‘‘confusion chorus’’. 
There is nothing in their behavior to suggest telepathy, or any mysterious type 
of psychic communication. Indeed a practised observer is often able, by not- 
ing the nature of the initial stimulus, to anticipate the reaction of the flock, 
although it is hardly to be supposed that he has for the moment become iden- 
tified with what Newland (loc. cit.) has called the ‘‘group soul.”’ 
The movements of a flock of English Sparrows when unmolested are sim- 
ilar in certain respects to those of a band of Bush-tits; a few birds take the 
lead and the others follow. Kessel (1921) has observed that the California 
Valley Quail are ‘‘stimulated to flight by the leader,’’ which he suggests 
further on may be any member of the flock that takes the initiative for the 
moment. It is stated by Woodward (1921, p. 138) of the collective soaring 
of gulls that ‘‘they start with perhaps a dozen or two birds, but these are soon 
Joined from all directions by other gulls in two’s and three’s until 100 to 200 
birds are in the air at once’’. Thus the spread of impulse through the group 
