1897.] Methods in Economie Ornithology. 393 
The method of field work, which requires the united efforts 
of a botanist as well as an entomologist, yields results which 
must not be considered a final solution to the problem, but 
only a contribution to our knowledge. Nevertheless, field 
work is indispensable, since many interesting facts may be 
learned by going to fruiting trees or shrubs and watching the 
birds that visit them. This sort of work can be done toa 
limited extent in a field where grasshoppers are abundant; 
but with small insects this method of observation is almost 
impossible. Even if all the different kinds of food eaten could 
be ascertained in the field, the result would still be unsatis- 
factory, for the proportions of the various constituents would 
be unknown, consequently any economic conclusions would 
be impossible. The examination of the contents of the stom- 
ach is the “court of final appeal,” because here the propor- 
tions of the different elements of the food can be determined. 
In researches in economic ornithology, under the direction of 
Dr. C. Hart Merriam of the U. S. Department of Agriculture, 
I have examined the stomachs of some 200 catbirds, and found 
that about half of this bird’s food is fruit, while the other half 
is insects. Beetles and ants form the most conspicuous part 
of the insect food, and grasshoppers and smooth caterpillars 
rank next in importance, while spiders, myriapods and bugs 
are frequently eaten. 
Although this method of stomach examination shows con- 
clusively what has been eaten, it neither tells what has been 
refused nor does it give the preferences of a bird for one kind 
of food over an other. The reason for this is that the different 
elements of the food supply where the stomachs were collected 
is unknown. To obtain such a knowledge of the accessible 
food supply, and to learn just what insects and berries the 
birds had an opportunity of eating, I took an excursion on 
July 30, 1895, to one of the many gullies which intersect the 
bluff overlooking the estuary of the Potomac, to make obser- 
vations on the feeding habits of the catbirds, and to collect 
data and material of the available food supply. The particu- 
lar gully chosen was about eighty yards wide by twice as long, 
* Prof. F. E. L. Beal. 
