The tyrant flycatchers (Tyrannidae) are a family of passerine birds which occur throughout North and South America. They are considered the largest family of birds known to exist in the world, with more than 400 species. They are the most diverse avian family in every country in the Americas, except for the United States and Canada. The members vary greatly in shape, patterns, size and colors. Some tyrant flycatchers may superficially resemble the Old World flycatchers, which they are named after but are not closely related to. They are members of suborder Tyranni (suboscines), which do not have the sophisticated vocal capabilities of most other songbirds.
A number of species previously included in this family are now placed in the family Tityridae (see Systematics). Sibley and Alquist in their 1990 bird taxonomy had the genera Mionectes, Leptopogon, Pseudotriccus, Poecilotriccus, Taenotriccus, Hemitriccus, Todirostrum and Corythopis as a separate family Pipromorphidae, but although it is still thought that these genera are basal to most of the family, they are not each other's closest relatives.
Species richness of Tyrannidae, when compared to habitat, is highly variable, although most every land habitat in the Americas has at least some of these birds. The habitats of tropical lowland evergreen forest and montane evergreen forest have the highest single site species diversity while many habitats including rivers, palm forest, white sand forest, tropical deciduous forest edge, southern temperate forest, southern temperate forest edge, semi-humid/humid montane scrub, and northern temperate grassland have the lowest single species diversity. The variation between the highest and the lowest is extreme; ninety species can be found in the tropical lowland evergreen forests while the number of species that can be found in the habitats listed above typically are in the single digits. This may be due in part to the fewer niches found in certain areas and therefore fewer places for the species to occupy.
Tyrannidae specialization among habitat is very strong in tropical lowland evergreen forests and montane evergreen forests. These habitat types, therefore, display the greatest specialization. The counts differ by three species (tropical lowland evergreen forests have 49 endemic species and montane evergreen forests have 46 endemic species). It can be assumed that they both have similar levels of specialization.
Regionally, the Atlantic Forest has the highest species richness with the Chocó following closely behind.