July, 1921 THE FLOCK BEHAVIOR OF THE COAST BUSH-TIT 123 
direction of movement, and numbers, either actual or estimated. I find these 
observations to agree with my assumption of three flocks, one large, the other 
two smaller and of nearly equal size. 
It is manifestly impossible to be absolutely certain that flocks of similar 
size observed in the same region at different times are identical; but repeated 
observation has given the impression very strongly that the flocks observed 
in February are in general the same ones seen in August preceding, though 
individual birds probably sometimes pass from one flock into another. I may 
add that I have never observed the Bush-tits more than one hundred yards 
up along the sides of a canyon, and it may be that relatively small hills, espe- 
cially when sparsely clothed with vegetation, form to them a somewhat effect- 
ual barrier. I think it extremely unlikely, for instance, that the number of 
birds in Strawberry Canyon would be augmented by an invasion of Bush-tits 
from Claremont Canyon, or vice versa. The topography of the region fur- 
nishes additional reason for believing that the birds I have had under observa- 
tion are limited to the narrow range which I have assigned to them. 
I early noted that, as Swarth (1914, p. 501) has observed, the Bush-tits 
appear with considerable frequency in certain tracts of trees and bushes on 
the campus, so as to suggest the possibility of their having definite forage 
routes, which are covered at more or less regular intervals. Working on this 
hypothesis, I undertook to map out the forage routes of the different flocks, 
and, by taking note of the intervals at which they recurred at certain definite 
points, I thought perhaps to be able to prepare a schedule of their movements. 
At first I seemed to have some degree of success with this part of the work, 
and on one or two occasions I was able to predict the whereabouts of a par- 
ticular flock from my hypothesis, and to find the birds exactly where I had 
expected them. But frequent subsequent failures have led me to conclude 
that success on these occasions was entirely accidental; and as I now look 
through my notes, I am unable to trace out anything approaching systematic 
progression over a well defined route. Any impression of regularity in the 
movements of the birds is doubtless due to mechanical causes, such as rela- 
tive density of shrubbery and other foliage in different parts of the range. 
A method of observation to which I have been partial is that of attaching 
myseif to a particular flock of Bush-tits and following it about for a consider- 
able period of time. For purposes of illustration, I wish to record in some 
detail the wanderings of a flock observed in Strawberry Canyon on February 
11. A map of the region in question has been introduced (fig. 24), which 
should be consulted in interpreting the following account. 
9:35 A. M.—Flock of 16 Bush-tits observed at A. Foraged through bushes to B; 
5 birds crossed road to C, then straggled back again to B, then to D; one returned to 
C and foraged alone for several minutes, then was joined by 6 others. The remainder 
of the flock retraced to A, then moved on to EK, to be followed shortly by the stragglers 
at C. The entire flock then moved across the road to F, which marks the edge of a 
small but dense thicket. 
From F the flock foraged in a leisurely fashion through to the east side of the 
thicket at G, then along its edge to J. At G one bird left the flock and crossed to H. 
where it foraged about 8 minutes, then rejoined the flock at I. From J the entire flock 
then retraced to I, crossed over to H, then moved slowly on to K and finally L, wkere 
they foraged in a live oak for a considerable period of time. At * one bird flew down 
and foraged for a few moments in the grass, a quite unusual type of behavior, which 
I have seen on only one other occasion. 
