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206 THE CONDOR Vol. XIII cleared away and the weeds allowed tO grow, Brewer sparrows were exceedingly common. During an early morning walk through brush and forest the following birds were seen: blue-fronted jay, Brewer sparrow, green-tailed towhee, western house wren, bush-tit, Calaveras warbler, western robin, red-shafted flicker, and Lewis woodpecker. Within the space of three-quarters of an hour, five different species of birds were seen ?o perch in a dead cedar on a small hill. The tree was first visited by a Bullock oriole, then by a small flock of western bluebirds, four other Bullock orioles, two cliff swallows, Which perched on the topmost limb, several purple finches and an evening grosbeak. In a little meadow west of Sisson, where grass and weeds grew in abundance, a large number of birds were seen. In the weeds green-backed goldfinches and Brewer sparrows were feeding in large flocks. Several flickers were feeding on the ground. A lazuli bunting flew into a fir tree where several Calaveras warblers were at work. A sparrow was heard in a nearby tree. Several robins flew from one tree to another. A western bluebird was perched on a stump. With the plague-ridden territory inhabited by so large a number of species of birds and by so large a bird population, it may at first seem strange that only five species of birds were found to. feed on Eu?onfa calf. romich. The investigation showed that only the-larger birds fed on the butterfly. Certainly most of the small birds are ill-adapted for catching insects as large as the butterfly in question. Their most intimate relation to the outbreak was doubtless when the insect was in the larval and pupal stage. If all the birds smaller than the Say phoebe be elim- inated from the list as being unable to act as checks on the butterfly, we find that over twenty-two percent of the species of the larger birds fed upon the butterfly. If we eliminate those of the larger birds, which ju?dging from their food habits would not feed upon the butterfly, we find that almost forty percent of the possi- ble species did feed upon the insect. A strikh?g fact is that the birds acting as checks, With one exception, that of the Say phoebe, are birds about whose depredations there is considerable complaint by the farmers of the state. That the blackbird, meadowlark, jay, and kingbird all do a certain amount of harm is undeniable, but too often only one side of the question is emphasized. Especial attention is called to the fact that even such a bird as the blackbird, which is often classed as the worst pest of the farmer, may become of value at times and places where it is least expected. The present paper shows that the same birds that are often classed as harmful may be very beneficial in the checking of an insect outbreak. Even though the brush attacked by the larva of Eu?o?i? c?ff. for?? is seldom killed by the defoliation, yet the plants must be weakened to some extent. If the economic value of the brush be measured by ils use as forage for deer and sheep, it will be seen that some importance, at least, attaches to this particular insect out- break in that the defoliation took place during the summer when it was most needed as forage. The economic importance or non-importance of the outbreak, however, in no way affects the value of the principle involved in the relation of the birds to the epidemic; namely, that birds prey upon the insect food most abundant and therefore become factors in the checking of an insect outbreak. In the life history of such an insect as ?u?o?fa af.for?fca, we find the maxi- mum number of individuals soon after hatching beg'ins in the spring. From this time on there is normally a rapid decrease in numbers. The decrease is due to, not only the action of birds, which are perhaps the most constant factor in the de-