WESTERN FLYCATCHER. Empidonax difficilis difficilis Baird

Field characters.—Similar to those for Wright Flycatcher (which see). Upper surface of body olive green, under surface definitely yellowish; lower mandible wholly yellow beneath. Voice: Call note a clear shrilly whistled swee'ip; song, a shrill, three part, see'rip, sip, see'rip, repeated at short intervals.

Occurrence.—Sparse summer visitant to Transition Zone on west side of Sierra Nevada. Observed in Yosemite Valley from May 1 (1916) to July 30 (1915), at Merced Grove Big Trees, and along Smith Creek (east of Coulterville). Frequents chiefly wooded cañon bottoms where incense cedars and alders line the streams. Forages singly, and perches 10 to 25 feet above the ground.

We found the Western Flycatcher to be rare and local in the Yosemite region, and restricted to the Transition Zone. A single individual was noted at the McCarthy Ranch (altitude 3200 feet) at the beginning of the forest, 3 miles east of Coulterville, and Mr. Donald D. McLean has record of a nest at Dudley, a short distance farther east. Two individuals were seen at Merced Grove Big Trees. All our other records pertain to Yosemite Valley, one of which, made at 5700 feet, on the Yosemite Point Trail, marks the highest place at which the species was observed. Seasonally the records range from May 1 (1916) to July 30 (1915), both dates for the Valley itself. To judge from observations in other parts of California, it seems likely that the birds arrive somewhat earlier and depart later than the limiting dates just given. Our observations on the floor of Yosemite Valley were not continuous during the seasons of migration.

The Western Flycatcher exhibits the same traits in posture and forage habits as do other members of the flycatcher family. When on the lookout for insects, an occupation which fills most of its waking hours, it sits on some twig in erect rather than horizontal posture and there turns its head from side to side, darting out in rapid flight after any suitable insect which may chance to pass close at hand. The Western Warbling Vireo and the Cassin Vireo, which live in the same sort of territory, bear a superficial resemblance in size and coloration to the Western Flycatcher; but their voices and manner of foraging are totally unlike the flycatcher's, so that there is no need to confuse these birds with this or with any other of the flycatchers.

On the morning of June 3, 1915, a Western Flycatcher was watched as it sang and foraged among the big-trunked incense cedars and huge mossy boulders on the north side of the Yosemite Valley, at the foot of Rocky Point. The greenish yellow of the bird's upper plumage and its yellowish under surface were the only sight characters available, but the call note and song were both distinctive. The former was a single high-pitched, even piercing, swee'ip or twee'it; less often a fainter peet was uttered. The song proper goes see'rip, sip, see'rip, or sometimes see'rip, sert, sip, see'rip, and is repeated over and over again, often so continuously that the pauses between songs seem no greater than the intervals between the constituent notes. The syllables were given in varying order, and often the single combination, see'rip, was uttered over and over again. While singing, this bird was perched on various twigs and branches 10 to 20 feet above the ground. The song is to be heard most often in May and early June, but as late as July 30 a bird was heard in full summer song.