Associated with flocks of the Mexican Bluebird (_Sialia, mexicana_), which was, by the way, the only kind of Bluebird observed, was always to be found one and sometimes two representatives of the Olive Warbler (_Peucedramus olivaceus_). The Bluebirds were generally feeding on some insects in the tall pines, in flocks of from six to ten individuals. The Olive Warblers were on the best of terms with their blue friends, and as the Bluebirds were shy and restless they made it difficult to obtain or observe very closely their smaller allies. I did not in these pine woods see the two species apart, and became at length so well aware of the intimacy that existed between them, that I would fire at any small bird passing high overhead in company with Bluebirds. They were chance shots, certainly, but the only two small birds obtained flying in this way with the Bluebirds were Olive Warblers. * * * Generally they preferred the largest branches of the pines when they alighted, though I took one not more than three feet from the ground in a small bush. Their movements while feeding or searching for food are very deliberate, though I noticed now and again certain motions when at the extremity of a bough that reminded me of a Kinglet or a Titmouse. Swarth (1940) says: "Though frequenting the tree tops to a great extent, they seem singularly tame and unsuspicious, and several times I have had one feeding in some of the lower branches, within arm's reach of me, without its showing the least sign of fear." _Voice._--The olive warbler has a rather loud, attractive, and distinctive note, but few observers have referred to it as a song. The "beautiful song" mentioned above consisted of "detached, melodious, whistling notes." One of its whistling notes sounds very much like the _peto_ note of the tufted titmouse and might easily deceive the listener. Scott (1885) observed that these warblers "had a call-note so like that of their associates [the bluebirds] as to be almost identical. It seemed to me only a clearer whistle of more silvery tone." Price (1895) saw a male alight on a twig near his mate, during nest-building, uttering "a liquid _quirt, quirt, quirt_, in a descending scale." Mr. Henshaw (1875) heard "a few strange Vireo-like notes coming" from an olive warbler. A bird that Dr. W. P. Taylor (MS.) watched in apparent courtship gave "a whistled call with descending inflection."