It’s the lucky individual who happens upon a Black-throated Blue Warbler’s nest while it is in use, for these birds tend to build their nest directly under leaves which keep the nest very well hidden. Now that many of the leaves have fallen off shrubs and saplings, where Black-throated Blue Warblers typically build their nests, they (nests) are especially noticeable, being at eye level or below.
The female warbler builds the nest, using a variety of material including white and yellow birch bark for the outer layer (glued together with spider silk and saliva), shredded bark fibers for the inner wall and fine black rootlets, pine needles, bits of moss and strands of mammal hair (horse, skunk, human, moose, porcupine and deer) for the lining. This combination of material makes their nest very distinctive and relatively easy to identify.
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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