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198 THE CONDOR Vol. XIII Although no damage was done to crops, the outbreak furnished a splendid opportunity to study the relations of the birds in eheek. ing such a plague of insects. As the Fish and Game Commission is carrying on at the present time an investiga- tion into the food habits of California birds in their relation to agriculture, evi- dence as to the part played by birds in this particular outbreak seemed to be of importance. Consequently an investigation was instituted under the auspices of the Commission. The writer spent a week during the latter part of August at Sisson, Siskiyou County, collecting data by field observation and by the collection of birds for analysis of stomach contents. A total of sixty-one specimens, representing twenty- one species of birds, are at hand for st6maeh examination. A list of the species identified during the stay totals forty-five. It is to be regretted that a larger num- ber of specimens representing a larger number of species is not at hand for exam- ination, for the greater number would, without doubt, have not only augmented the number of species found to feed on the insects, but would also have established points now in doubt. To insure a complete understanding of the outbreak, a brief account of the life hisi:ory and habits of the insect in question, follows. As far ag can be ascertained, the butterfly which has been so abundant in the north this year, has no common name. Among scientists it is known as ?'u?onia californica. It is closely allied to the members of the genus l/?nessa, the tortoise-shell 'butterflies, species of which are known throughout the United States. ?'uvanessa cardui, a common butterfly of southern California appeared a few years ago in a swarm almost equal in extent to the plague of Eu?ona cal?fornica. There are four stages in the life of every butterfly and moth, egg, larva, pupa, and imago. From the egg hatches a eaterpillar or larva. It is only in the larva stage that a butterfly or moth becomes of eeonmnie importance: nearly all of their larvae feed on vegetation. The depredations of the army worm, which is simply the larval form of a moth, are known only too well. The larva lives for some time on vegetation, then either hangs itself head down and is transformed into a chrys- alis, spins a cocoon, or buries itself in the ground. This is called the pupa stage. After a week or more in this state there emerges the imago or adult form, a but- terfly or moth. The butterfly or moth usually lives for several months or even for a year, then lays its eggs and the cycle is begun over again. t?ugona cal[fornca lays its eggs on a common shrub of the mountains known asthorn brush, deer brush, buck thorn, buck brush, or snow brush (Ceanolhus cordulatus and Ceanolhus velulinus). In the early spring the larvae hatch from the eggs, crawl out on the foliage and begin to feed on the leaves. At the present time there are large areas in Siskiyou County where this brush is entirely defoli- ated as a result of the work of these larvae (see fig.67). By the middle of the summer, they have grown to be an inch or more in length and are ready to pupate. They then hang themselves head down on the under side of the branches and become pupae. In the defoliated areas, great numbers of pupae were found hanging from the un- der sides of the branches. Most of them were mere shells, as the butterfly had hatched, but large nmnbers were also found which had apparently been destroyed by birds and by parasites (see fig.69). A large hole picked into the thoracic portion of the pupae evidently showed the work of birds, whereas small round holes for the entrance and departure of some insect, gave evidence of the work of a parasite. Inside of a few weeks the butterfly or imago form emerges. Its food consists of what moisture and sap it can suck up on vegetation. The butterflies may possibly