126 THE CONDOR Vol, XXIII 
It should be noted in this connection that Trotter (1916, p. 29) has attrib- 
uted a similar type of behavior to the mammalian herd: ‘‘Kach member of the 
flock tending to follow its neighbor, and in turn to be followed, each is in 
some sense capable of leadership’’. 
2. The line of flight between two locations is usually determined by the 
first adventurer. Ordinarily it represents the shortest distance across an open 
space. The other birds gather at the point of departure and follow suit, pos- 
sibly through imitation, or because the tested route appears the safest. 
3. Sometimes two or three self-appointed leaders move off simultaneously 
in different directions. It seems then to be largely a matter of caprice which 
one the flock follows. Each leader may have a following, and the flock for a 
time become divided into two or three segments; or the flock may follow any 
one of the leaders. In any case a bird which ventures into a new location and 
is not followed by others soon. loses its wanderlust and hastens to rejoin its 
comrades. 
4. Individual birds which are finding good foraging may lag behind 
until the flock is some distance away. Then they appear suddenly to wake up 
to the fact that they have been left alone, and hurry after the flock with ex- 
cited calls. Occasionally these loiterers become lost entirely; thereupon they 
become greatly agitated, and move rapidly from place to place, uttering the 
location note so loudly and continuously that I have sometimes mistaken the 
notes of a single bird for those of an entire flock. It is extremely probable 
that such lost birds attach themselves to the first flock they find, regardless of 
whether or not it is the one of which they originally formed a part. 
5. At more or less frequent intervals the flock tends to become assembled 
in a relatively small space, the branches of a single oak, for example, and 
there to pause long enough for stragglers to catch up. It will be seen by ref- 
erence to the observations above recorded that such reunions occurred at points 
E, J, and Q. This type of behavior is probably unmotivated, and may even 
be due to mechanical causes, such as the nature of the forage route; but it is 
of frequent occurrence, and probably is of considerable importance in keeping 
the flock together. 
6. Call notes play an important role in flock behavior (cf. Grinnell, 
1903). The principal notes are a location note, uttered more or less continu- 
ously, which functions in keeping the flock together while foraging, an alarm 
note, and a ‘‘confusion chorus’’ which is uttered by all members of the flock 
in concert on the appearance of certain enemies, e. g., a Sharp-shinned Hawk. 
7. The method of flock movement makes evident the extreme improba- 
bility of there being any definite forage routes. The direction taken by the 
flock at any time is a matter of caprice, or the circumstances of the moment. 
Due to their dislike for crossing open spaces, however, the birds are likely to 
frequent areas where the vegetation is continuous and will generally avoid 
those where it is discontinuous, so that an impression of regularity. in their 
forage movements may thus secondarily be given. 
Whether or not the differences between the flock behavior of the Bush- 
tit and that of various other birds manifesting a more complicated type of 
flock organization .are differences of kind or of degree only, is a subject for 
further investigation. There is a field here for much interesting and profita- 
ble work, and it is the belief of the writer that such studies are likely to be 
