Eggs.—Either 3, 4, or 5 eggs are the numbers in the few recorded sets. The 5 eggs in the Thayer collection are ovate and have only a slight gloss. The white ground color is speckled and spotted with tones of “bay,” “auburn,” “chestnut brown,” “Mars brown,” or “russet,” with undertones of “pale brownish drab,” or “vinaceous drab.” Some of the eggs have markings of two or three shades of the darker browns, such as “bay,” or “auburn,” while others have tones of a single lighter brown, such as “russet,” interspersed with the drab spots. There is not a well defined wreath on any of these eggs, although the spots are denser at the large end. The measurements of 40 eggs average 17.4 by 12.9 millimeters; the eggs showing the four extremes measure 19.0 by 12.7, 17.3 by 13.6, 15.2 by 12.7, and 17.4 by 12.3 millimeters (Harris).
Plumages.—Maj. Allan Brooks (1934) gives the following good description of the juvenal plumage of Townsend’s warbler: “Upper surface brownish olive, greener on dorsum and grayer on crown; lores and auriculars dusky brown, a broad supercilium and malar stripe whitish, faintly tinged with yellow; chin and throat dusky olive gray passing into white on the ventral region and crissum, the flanks and breast streaked with dusky; wings with two white bars formed by the tips of the greater and lesser coverts, tertials edged with ash gray, the black central shafts of the white bars seen in the second (first winter) plumage are barely indicated; tail as in second plumage.”
Evidently the juvenal plumage is worn for only a very short time, for in the bird thus described, collected on July 7, “a few yellow feathers of the second plumage are appearing.” Apparently, the postjuvenal molt is completed in July and August, and involves the contour plumage and the wing coverts only.
The young male in first winter plumage is similar to the old male at that season, but with less black on the head and throat, cheeks more olive, black streaks on back and sides obsolete, and yellow of the throat paler. The young female differs from the adult female in a similar way. There is evidently a partial prenuptial molt in late winter or early spring, but I have not been able to trace it. Apparently the black throat is acquired by the young male at this molt, and perhaps enough of the head and body plumage to make the young bird appear nearly adult, though the worn and faded juvenal wings and tail will distinguish it.
Adults have a complete postnuptial molt in July and August. Ridgway (1902) describes the fall and winter male plumage as “similar to the spring and summer plumage, but all the black areas much broken or obscured; that of the pileum and hindneck by broad olive-green margins to the feathers, the black forming mesial or central streaks, that of the auricular patch overlaid by olive-green tips to the feathers, and that of the throat replaced by nearly uniform lemon yellow, with black appearing as spots or blotches on sides of chest; black streaks on back, etc., more or less concealed.” The adult female fall plumage is “similar to the spring and summer plumage, but upper parts slightly browner olive-green, with the streaks obsolete, or nearly so; sides and flanks tinged with brownish.”
Although considerable wearing away of the concealing tips of the feathers occurs during the winter, thus brightening the nuptial plumage, there is evidently at least a partial prenuptial molt, especially about the head and throat, at which the clear black throat of the male is assumed and perhaps more of the body plumage renewed.
Stanley G. Jewett (1944) describes four specimens of adult males that are clearly hybrids between this species and the hermit warbler.
Food.—Professor Beal (1907) examined the contents of 31 stomachs of Townsend’s warblers taken in California from October through January, of which he says: “The animal food consists of insects and a few spiders, and amounts to over 95 percent of the food during the time specified. Of this, bugs make up 42 percent, mostly stink-bugs (Pentatomidae) and a few leaf-hoppers and scales.” Several stomachs were entirely filled with stink-bugs.
Hymenoptera, consisting of both wasps and ants, are eaten to the extent of 25 percent of the food. Most of them are winged species. Perhaps the most striking point in the food of this bird is the great number of weevils or snout-beetles represented. They amount to over 20 percent of the food, while all other beetles form less than 1 percent. The greater number of these insects were of the species Diodyrhynchus byturoides, a weevil which destroys the staminate blossoms of coniferous trees. Five stomachs contained, respectively, 68, 65, 53, 50, and 35 of these beetles, or 271 in all. * * * Representatives also of another family of snout-beetles very destructive to timber were present in a few stomachs. These were the engravers (Scolytidae), which lay their eggs beneath the bark of trees, where they hatch, and the larvae bore in every direction. Caterpillars and a few miscellaneous insects and some spiders make up the remainder of the animal food.