Systematics
The four genera of these birds make up the family Vireonidae, and are believed to be related to the crow-like birds in family Corvidae and the shrikes in family Laniidae. Recent biochemical studies have identified two babbler genera (Pteruthius and Erpornis) which may be Old World members of this family (Reddy & Cracraft 2007). Observers have commented on the vireo-like behaviour of the Pteruthius shrike-babblers, but apparently no-one suspected the biogeographically unlikely possibility of vireo relatives in Asia.
The family can be conveniently though perhaps inaccurately categorised by genus as the true vireos, the greenlets, the shrike-vireos and the peppershrikes. Preliminary genetic studies by Johnson et al. revealed large interspecific genetic distances between clades within Vireo and Hylophilus of a similar magnitude to differences between Cyclarhis and Vireolanius. Furthermore some vireo and greenlet species may be closer to the peppershrikes than to their respective congeners. A more comprehensive study may reveal this family to be considerably undersplit at both the generic and species level.
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