Spring.—The sycamore yellow-throated warbler is one of the earliest wood warblers to enter the United States from its winter home, arriving in Louisiana around the first week in March, reaching Indiana about the middle of April, and appearing in Michigan as early as April 20. In Ohio, according to Dr. Wheaton (1882), "this is the first of the family to arrive in spring. It is always to be seen before the Yellow-rumped and Yellow Warblers make their appearance, sometimes before the last snow and ice. I have seen them in considerable numbers on the 13th of April, and have known of its occurrence as early as April 9th. When on their migrations they confine themselves almost exclusively to the trees which skirt the streams, and move northward by day with considerable rapidity.”
The main migration route seems to be almost directly northeastward, from western Mexico and Central America to western North Carolina and Ohio, and more directly northward through the broad Mississippi Valley to Michigan and Wisconsin. This is markedly different from the migration route of the eastern race, which migrates nearly northward along the Atlantic coast.
Nesting.—Whether the nest of the sycamore warbler is in a cypress or in a sycamore, it is always placed at a considerable height from the ground, for this is a tree-top bird. Nests have been recorded at heights ranging from 10 to 120 feet above the ground, but probably most of them are between 30 and 60 feet up. Mr. Butler (1928) describes two Indiana nests of similar construction. One was—
built about 35 or 40 feet above the ground in a flat crotch, on an approximately horizontal limb of a large sycamore tree. * * * The nest measures as follows: Outside diameter 2.50 inches; inside diameter 1.65; outside height 2 inches; inside depth 1.75 inches. The heavier frame was composed of shreds of grapevine bark, bits of the covering and coarser fibre of weeds, mingled with which were many small pieces of cotton cord or ravelings. The nest was lined and its entire bottom was composed of the soft down obtained from dry sycamore balls. In fact the nest really had no foundation for the bottom, the lining material reaching through to the limb. [The other] was about 75 feet above the ground in a crotch of small branches toward the end of a sycamore limb which was not strong enough to bear one’s weight. It was so hidden by the foliage that it could not be seen until some of the leaves fell this autumn.
A set of four eggs is in the Richard C. Harlow collection, taken by W. C. Avery, Greensboro, Ala., April 24, 1893. The nest was in a liquidambar tree, 26 feet up and 9 feet out from the body of the tree, on a horizontal branch and nearly concealed in the Tillandsia in which it was built. George Finlay Simmons (1925) says that in Texas the nests are sometimes built in an elm or a pecan tree, from 12 to 35 feet from the ground.
Eggs.—The sycamore warbler lays from 3 to 5 eggs; in most cases 4 eggs seem to complete the set. Mr. Simmons (1925) describes them as “dull greenish gray-white; marked with distinct and clouded blotches, specks, and under-shell markings of lavender, purplish-gray, umber, and brownish-red; and sometimes even blackish spots; usually wreathed about the larger end.” The measurements of 10 eggs average 16.9 by 12.7 millimeters; the eggs showing the four extremes measure 17.6 by 12.1, 16.2 by 12.8, and 16.6 by 13.0 millimeters.
Plumages.—The sequence of plumages and molts is probably the same as for the yellow-throated warbler.
Food.—Very little seems to have been published on the food of this warbler, but it probably does not differ materially from that of the other wood warblers. Professor Aughey (1878) found remains of 15 locusts and 24 other insects in the stomach of one collected in Nebraska. A. H. Howell (1924) says: “Examination of 9 stomachs of this bird from Alabama showed its food to be mainly flies, beetles, ants and other Hymenoptera, and spiders.”
Behavior.—Ridgway (1889) says that “in its motions, this warbler partakes much of the character of a creeper, often ascending or descending trunks of trees or following their branches, much in the manner of a Mniotilta.” Butler (1898) says that “its longer flights much resemble those of the Chipping Sparrow. Its shorter ones, as with quivering wings it beats rapid strokes when moving from limb to limb, remind one of the movements of the Kingbird.” Referring to its general habits in Texas, Simmons (1925) says it is:—
observed singly or in pairs, moving very slowly about in the tops of the trees, particularly the sycamores along streams, carefully keeping limbs and branches between itself and any chance observer. Movements very deliberate, sometimes stopping for several minutes, creeping along by small hops, among upper branches, never on trunks or larger limbs; thus, in actions, strikingly different from most members of the warbler family. Usually keeps to the tops of the tallest trees; hops from one perch to another very slowly; occasionally comes down among the lower branches. Usually quiet, the song being uttered at wide intervals; however, at times in spring it may be heard almost constantly singing.