The blue-gray gnatcatcher, Polioptila caerulea, is a small active bird that is widely distributed throughout much of the United States and Mexico. It breeds in a variety of forest habitats in the United States south of the Great Lakes, from the Texas panhandle to the east coast, in the Great Basin, and in parts of California. Individuals wintering in most of the United States migrate south to wintering grounds in Mexico and Cuba. Individuals breeding in Bermuda and parts of Mexico and Florida remain in the same area year-round. The blue-gray gnatcatcher is a common summer resident in pinyon-juniper forests of southern Utah; it is less common in northern portions of the state.
Blue-gray gnatcatchers are territorial, and both sexes will challenge intruders. Individuals begin a challenge by adopting an aggressive posture to communicate their displeasure. Their tails are capable of moving in a number of positions, and much can be communicated through the positioning of the tail. If intruders remain, individuals will take chase, and fighting will ensue shortly thereafter.
Blue-gray gnatcatchers eat insects and spiders which they glean off foliage and occasionally catch while hovering. Pairs are monogamous, and the male substantially contributes to the preparations for, and care of, the young. The male and female construct a cup-shaped nest out of plant materials, line it with spider silk, and then cover the outside with fine, soft materials. Four to five eggs are incubated, and the male and female share the nest sitting duties equally. Hatchlings are blind, immobile, and featherless. The female generally stays with the hatchlings in the nest, while the male brings food for the young. The hatchlings leave the nest after about ten days, but the parents continue to feed them for another two weeks. Pairs commonly have second broods during a breeding season.