A bird of open country, Say's Phoebe is similar in behavior, size, and breeding biology to the Black (Sayornis nigricans) and Eastern (S. phoebe) phoebes, although its voice, coloration, and habitat preferences are distinctive. Dawson (Dawson 1923) described its melancholy call as the most despondent of all the “pewees.” Its drab gray-brown back, black tail and cinnamon-colored belly fade into the sage brush plains, barren foothills, and rimrock country where this species resides. Say's Phoebe breeds over much of western North America, from the Great Plains west nearly to the Pacific coast. Indeed, it has one of the broadest latitudinal ranges among North American flycatchers, extending from central Mexico farther north than any other into the arctic tundra, apparently constrained only by lack of suitable nest sites.
In the fall, northern populations of Say's Phoebe migrate south and winter in the southwestern United States and central Mexico, overlapping with southern residents. Spring migration begins early for this bird, compared to other western flycatchers. It contends with cold weather and the scarcity of flying prey by hover-gleaning insects from the ground. Primarily insectivorous, it captures wild bees and wasps most frequently, but also flies, beetles, and grasshoppers, generally foraging from perches within 1–2 meters of the ground.
Like other phoebes, this species shows strong nest-site tenacity. Typically monogamous and frequently double-brooded, it builds its nest (under a protective ceiling) on a rocky ledge or other supporting shelf, which often includes human-made structures. It frequently nests in abandoned buildings among prairie farms and western ranches. Its nest, typically constructed of grass, stems, moss, and other fibrous plant materials, differs from that of the Black and Eastern phoebes in that mud is rarely used in its construction. Nest completion and egg-laying typically occur in mid-March in Texas and late May in Alaska. The female incubates the clutch of 4 or 5 eggs for about 15 days, and young fledge about 17 days after hatching.
Say's Phoebe is the least studied of the Sayornis group. Anecdotal accounts make up a large portion of the literature concerning this species, but important work on the species' breeding biology and behavior has been undertaken in Texas (Ohlendorf Ohlendorf 1971, Ohlendorf 1976), Nevada (Ackerman 1988), and Kansas (Schukman Schukman 1974, Schukman 1993). The dietary preferences of this species have been studied in some detail by Beal (Beal 1912) rangewide, Ohlendorf (Ohlendorf 1976) in Texas, and Rosenberg et al. (Rosenberg et al. 1991) in Arizona, and its foraging biology has received limited study by Ackerman (Ackerman 1988) in Nevada. Behavior and vocal communication remain poorly understood; limited attention was devoted to this species by Smith (Smith 1970f, Smith 1970g) in his studies of Sayornis communication and behavior. Almost no information is available on the population dynamics, demography, physiology, energetics, and nutritional requirements of this species.