ABSTRACT
Polioptilidae are a small, New World, mostly tropical family that is probably an offshoot of the Old World Warblers, and have previously been lumped into the broader Muscicapidae that included not only Old World warblers but also thrushes and several other Old World groups like monarch flycatchers. The three polioptilid genera are basically grouped into gnatwrens and gnatcatchers. Gnatwrens are typically understory-dwelling, long-billed, and clad in browns, whereas gnatcatchers are often canopy-dwelling, relatively short-billed, and clad in grays and blacks. North American gnatcatchers appear to all follow a Complex Alternate Strategy, in spite of some species with limited to no migratory tendencies. Microbates and Ramphocaenus also do not undergo obvious seasonal plumage transitions, and a prealternate molt may be unnecessarily in the shaded understory of the forest. The skull probably usually ossifies before the second prebasic molt SPB in adult polioptilids and is a useful aging tool, as molt limits are sometimes subtle and difficult to detect.
