1897,] Methods in Economie Ornithology. 395 
gully, one would, with a fair degree of accuracy, be able to 
predict what kind of food catbirds would eat in another gully 
that had absolutely the same food supply. And so one might 
perfect this line of research until he could tell just which of 
the objects a, b, c, d, e, f, g, h in the accessible food supply of a 
locality a given bird would select. 
Let this suffice for the combination of the field work method 
with that of the examination of stomach contents. Very often 
birds that are too shy to be watched in the field may be kept 
in captivity and then offered various kinds of food. Such ex- 
perimentation has proved a profitable adjunct to stomach ex- 
aminations. Among the birds that I have experimented with 
were four catbirds, which had been recently trapped in the 
vicinity of Washington, D. C. Among the first insects offered 
to my birds were a dozen spiny black caterpillars (Huvanessa 
antiopa). The birds, though hungry, refused these repulsive 
looking creatures. By the next morning the caterpillars that 
had crawled out of the cage had pupated. I put one of these 
pupe on the floor of the cage. It was eyed for some moments 
by a hungry bird and then devoured. Several days later the 
pupe hatched into the brown butterfly which is so common in 
early spring, and one of these having been given to the birds, 
they fought over it and each finally obtained part of the in- 
sect. Beetles and ants were next tried. In order to prevent 
them from escaping from the cage, they were put on a piece 
of cork, which was anchored in a large drinking bowl. The 
birds soon became accustomed to the cork island with its cargo, 
and when all the insects had been eaten, often rapped on the 
cork for more. Bad smelling beetles (Carabidx), which have 
been supposed to develop their stench to protect them from 
birds, were snatched as soon as they were put on the cork. 
Ants, which are highly flavored owing to the large quantity 
of formic acid which they contain, seemed te be regarded as 
choice food. Stink bugs (Pentatomidx), whose nauseating 
odor is familiar to every one who has been berrying, were 
eaten by the catbirds, even when they had been well fed with 
other food. Large hard shelled beetles, such as Passalus cor- 
nutus, were refused by the catbirds, but soft insects, such as 
