[Author’s Note: The measurements of 42 eggs average 15.8 by 12.4 millimeters; the eggs showing the four extremes measure 16.6 by 12.9, 16.5 by 13.0, 14.9 by 12.2, and 15.8 by 11.6 millimeters.]
Plumages.—[Author’s Note: Two young birds, just able to fly from the nest and taken by Wayne on May 13, are thus described by Brewster (1905):
The male which is now before me may be described as follows:—Top and sides of head and fore part of back faded hair brown with a trace of ashy on the middle of crown; remainder of upper parts dull olive green; wings and tail (which are fully grown) as in the first winter plumage excepting that the greater and middle wing-coverts are rather more broadly tipped with light brown, forming two well-marked wing-bars; chin and throat brownish white tinged with yellow; sides of jugulum smoke gray, its center yellowish; sides of breast gamboge yellow shading into olive on the flanks; middle of breast, with most of abdomen, yellowish white; under tail-coverts ashy white. All the feathers on the under parts which are strongly yellow or olive, and those on the upper parts which are decidedly ashy or greenish, appear to belong to the autumnal plumage or, as it is now called, the first winter plumage, but all the other feathers on the head and body are evidently those of the first plumage. * * *
I have not seen the young female Bachman’s Warbler above referred to, but Mr. Wayne writes me that “It differs from the male only in these respects: The yellow on the sides of the breast is very much paler and more restricted and the back is not greenish, but brownish. The white on the tail-feathers is merely indicated on the margins of the inner webs of the tail-feathers.”
It would appear from the above that there is a sexual difference even in the juvenal plumage, and that the postjuvenal molt begins before the middle of May. This molt evidently involves all the contour plumage and the wing coverts but not the rest of the wings or the tail. The young male in first winter plumage is similar to the adult male at that season, but the crown is entirely gray, or with very little black; the feathers of the black patch on the throat, which is more restricted, are tipped with yellowish or buffy. There are no specimens available that indicate a prenuptial molt, which is probably very limited. Young males in the first nuptial plumage may be recognized by the worn and faded wings and tail.
The complete postnuptial molt of adults apparently occurs in July or earlier; I have seen no molting birds, but a large series of August birds are all in completely fresh winter plumage. In this plumage the male resembles the spring male, but the black of the crown is widely tipped with gray and the black of the breast is narrowly tipped with yellowish; these tips largely wear away before spring, although Wayne (1910) says that his “breeding males all show the olive yellow edging on the black feathers.” Similar molts and changes take place in the female, but she has no black in the crown and much less or none at all on the breast; her colors are duller and she has less white in the tail, as well as olive-green, instead of yellow, lesser wing coverts.
For a full description of individual variations in plumage, the reader is referred to Mr. Brewster’s (1891) excellent paper.]
Food.—Very little information is to be found concerning the food of this warbler, but insects undoubtedly constitute its diet. Howell (1924) says: “Five stomachs of this species from Alabama contained remains of caterpillars and a few fragments of Hymenoptera, probably ants.”
Behavior.—Wayne (1907), in writing of this bird on its breeding grounds, says: “Bachman’s Warbler is a high-ranging bird, like the Yellow-throated Warbler, and generally sings from the top of a sweet gum or cypress. It appears to have regular singing stations during the breeding season, and upon leaving a tree it flies a long distance before alighting. On this account it is impossible to follow the bird through the dark forest, and it can only be detected by its song. I have occasionally seen the males in low gall-berry bushes within six or eight inches of the ground, but their usual resorts are among the topmost branches of the tallest forest trees.”
Brewster (1891) had similar experience with migrating birds in Florida: