Male and female Black-throated Blue Warblers differ strikingly in appearance, so much so that the two sexes were considered separate species by early naturalists, including John J. Audubon. While the male is a brilliant blue, the female is dull gray which makes her practically invisible when she’s on a nest.
Black-throated Blue Warblers have anywhere from one to three broods in a summer, the first usually in June, a second, if there is one, in July and rarely a third in late July or early August. The nest is usually within three feet of the ground, and is built out of thin strips of birch bark and bits of rotten wood bound together by cobwebs and saliva. Fibers, rootlets, needles and mammalian hair line the nest. Female Black-throated Blue Warblers are known for sitting tightly on a nest until a potential threat is very close, at which point they drop to the ground, and, similar to Killdeer, engage in a distraction display, feigning injury to their wing.
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