Food.—Professor Beal (1907) examined the stomachs of 383 Audubon’s warblers taken in California from July to May, inclusive. The food consisted of 85 percent of animal matter (insects and spiders) and a little more than 15 percent of vegetable matter. The largest item was Hymenoptera, 26 percent, consisting mostly of ants, with some wasps, and a few parasitic species. Diptera accounted for 16 percent, including house flies, crane-flies, and gnats, many of which must have been caught on the wing, as this warbler is a good flycatcher. Bugs, Hemiptera, amounted to nearly 20 percent of the food, including the black olive scale, other scales, plant-lice, stink bugs, leaf-hoppers and tree-hoppers. “Plant lice (Aphididae) were contained in 39 stomachs, and from the number eaten appear to be favorite food. Several stomachs were entirely filled with them, and the stomachs in which they were found contained an average of 71 percent in each.” Caterpillars amounted to nearly 14 percent and beetles more than 6 percent of the food; most of the beetles were injurious species. Other insects and spiders made up about 2 percent.
The vegetable food consisted of fruits, mostly wild and of no value, less than 5 percent, and seeds, over 9 percent, mostly weed seeds and seeds of the poison oak. These warblers have been known to puncture grapes and they probably eat some late fruit, but they do very little damage to cultivated fruits and berries. C. S. Sharp (1903) observed a flock of 200 birds, mostly Audubon’s warblers, greedily eating the raisins in the tray shed of his packing house; they had to be constantly driven away. Mrs. Amelia S. Allen says in her notes that they collect in great flocks in the live oaks to feed on the oak worms in the spring, and that they eat myrica berries in the fall. John G. Tyler (1913) says: “Audubon warblers share with Say Phoebes the habit of catching flies from a window, sometimes becoming so engrossed in this occupation as to cling for several seconds to the screen where a south-facing window offers a bountiful supply of this kind of food.”
Behavior.—Audubon’s warbler is a lively and active bird that seems to be always in a hurry, constantly moving in pursuit of its prey. Mrs. Bailey (1902) writes:
Its flight and all its movements seem to be regulated by gnats, its days one continuous hunt for dinner. When insects are scarce it will fly hesitatingly through the air looking this way and that, its yellow rump spot always in evidence, but when it comes to an invisible gauzy-winged throng it zigzags through, snapping them up as it goes; then, perhaps, closing its wings it tumbles down to a bush, catches itself, and races pellmell after another insect that has caught its eye. In the parks it is especially fond of the palm tops frequented by the golden-crowned sparrows, and dashes around them in its mad helter-skelter fashion. The most straight-laced, conventional thing it ever does is to make flycatcher sallies from a post of observation when it has caught its insect. If it actually sits still a moment with wings hanging at its sides, its head is turning alertly, its bright eyes keen for action, and while you look it dashes away with a nervous quip into midair, in hot pursuit of its prey.
It is not especially timid, being easy to approach when at its nest, and it shows its confidence in human nature by building its nest in trees in parks, over highways, in gardens, and even close to houses. Its behavior in the defense of its young shows a solicitude for their welfare. Jensen (1923) says: “If a nest with young is discovered, both parent birds try every means possible to draw the attention of the intruder away from the nest. Often I have seen them drop with folded wings from the top of a tree and flutter among the leaves as if each had a broken wing.” And Grinnell, Dixon, and Linsdale (1930) write:
June 15, 1925, a female Audubon warbler was seen which showed concern whenever the observer went near a certain thicket of very small pines and willows. The bird came to within three meters of the intruder and distracted his attention by going through an elaborate display. The bird spread its tail fan-wise, showing the white spots to greatest effect, and quivered the partly spread wings, toppling over backwards at the same time, as if unable to hold to the perch. For an instant the observer thought the bird’s foot was caught in the forking twigs. The inference finally made was that partly fledged young were in the low vegetation somewhere very near.
Voice.—Samuel F. Rathbun sends me the following note on the song of Audubon’s warbler: “The first note or two is given rather slowly, then its utterance is more rapid and with a somewhat rising inflection, the song closing a little hurriedly. It is quite a strong and sprightly song, but its charm lies mostly in the fact that it is one of the first, if not the very first, of the warbler songs heard in the spring. The call note given by both sexes is the same, a quick and slightly lisping one that is also used in the autumn and at times in flight.”
Dr. Walter P. Taylor (MS.) says of a song heard at Fort Valley, Ariz., on June 12, 1925: “The song seems much less full and seems lacking in quality, as compared with that of the Audubon in Washington State. It was so lacking in strength and quality that I took it for a Grace warbler.” He wrote it as wheetlea, wheetlea, repeated 7 or 8 times, or wheetoo, 7 times repeated, or again wheetleoo wheet, the final syllable a little different from the others.
Mrs. Bailey (1902) says: “His song is of a strong warbler type, opening toward the end, chwee, chwee-chwee-ah, chwee, between the song of the yellow warbler and that of the junco.” At Lake Burford, N. Mex., in May and June, according to Dr. Wetmore (1920), “males were found singing from the tops of the tallest pines and were slow and leisurely in their movements in great contrast to their habit at other seasons. Frequently while singing they remained on one perch for some time so that often it was difficult to find them. The song resembled the syllables tsil tsil tsil tsi tsi tsi tsi. In a way it was similar to that of the Myrtle Warbler but was louder and more decided in its character.”
Dr. Merrill (1888) says: “On two or three occasions I have heard a very sweet and peculiar song by the female, and only after shooting them in the act of singing could I convince myself of their identity.”