In the previous section it was shown that the
warblers feed in different places and in a different
manner, thus probably being exposed to different
foods for the first and second reasons mentioned
above. It is the aim of this section to show that
the rive warbler species have only small differences
of the third kind. Theoretically, such differences,
unaccompanied by morphological adaptations,
would be disadvantageous, for, lacking the adaptations required to give greater efficiency in food collecting, and suffering a reduction in the number
of acceptible food species, a bird would obtain
food at a lesser rate. When the necessary adaptations are present, they usually consist of quite marked differences in bill structure such as those
reported by Huxley (1942), Lack (1947), and
Amadon (1950). As Table V shows, the mean
bill measurements in millimeters of the five species
of warbler considered in this study are quite
similar. Twelve specimens of each species from
the Peabody Museum of Natural History at Yale
University were measured for each of the means
given.