The tyrant flycatchers comprise a family with unusually broad ecological radiation, but most are birds for which we have as yet very little information about even gross behavior patterns, and for which phylogenetic relationships remain uncertain. One group is ecologically interesting because its species forage in ways at least superficially analogous to wood warblers, vireos, titmice, wagtails, and Old World reed warblers and grass warblers. In many cases the tyrannids even resemble these other groups in plumage characteristics. This group falls within Hellmayr's (1927) subfamilies Serpophaginae and Euscarthminae. Although I shall argue in subsequent papers that these two subfamilies should not be distinguished, a large number of species and genera are involved and it is convenient to use Hellmayr's classification as a framework for presenting information about their behavior. Most of his serpophaginine species form a coherent phylogenetic group even if they appear to be as closely related to some euscarthminine genera as they are to each other. My studies began in 1959 and continued intermittently through 1969 when time was available from more intensive work with other tyrannid genera. The amount learned about the behavior of different species varies greatly, but some major patterns of display behavior (i.e., evolutionarily stylized signalling) and of behavioral aspects of ecology are now apparent. These permit reassessment of some relationships currently recognized (e.g., by Hellmayr 1927, Zimmer, MS, and de Schauensee 1966) at the generic level, and based in large part on characteristics available in museum skins. Because these characteristics (primarily bill and leg morphology and plumage pattern and coloration) relate to environmental parameters, knowledge of ecological behavior is pertinent to the interpretation of their systematic significance. Display characteristics add yet another dimension for comparison. The material is presented below by taking each of Hellmayr's genera, briefly describing the plumages and ranges of its species, seeking similarities and differences in general habitat preferences and foraging methods, then considering the vocal and visible displays. Dislays are given capitalized names in accordnce with established ethological procedure, and are described and compared in physical form and employment, emphasizing similarities an differences among displays that are used i similar ways (i.e., accompanied by compa able behavior patterns) by different species. Through what is now known about the employment of displays in tyrannid genera where whole repertoires have been much more thoroughly studied (e.g., Tyrannus, Smith 1966; Sayornis, Smith 1969b, 1970a, b; Contopus, Myiozetetes, Pitangus, and Myiodyna tes, Smith, MS), it is possible to estimate what kinds of serpophaginine displays have been sampled. Further, studies of members of et other Hellmayrian subfamilies such as the Eu carthminae (Smith, unpubl. data) and Fluvicolinae (Smith 1967, 1970c, 1971) permit the forms of these displays to be considered within a broader perspective.