The differences in feeding behavior of the
warblers can be studied in another way. For,
while all the species spend a substantial part of their time searching in the foliage for food, some
appear to crawl along branches and others to hop
across branches. To measure this the following
procedure was adopted. All motions of. a bird
from place to place in a tree were resolved into
components in three independent directions. The
natural directions to use were vertical, radial, and
tangential. When an observation was made in
which all the motion was visible, the number of
feet the bird moved in each of the three direc
tions was noted. A surpringing degree of di
versity was discovered in this way as is shown in
Figure 7. Here, making use of the fact that the
sum of the three perpendicular distances from
an interior point to the sides of an equilateral
triangle is independent of the position of the point,
the proportion of motion in each direction is re
corded within a triangle. Thus the Cape May moves predominantly in a vertical direction, black throated green and myrtle in a tangential direction,
bay-breasted and blackburn ian in a radial direction. To give a nonparametric test of the significance of these differences Table III is required.