Verdin (Auriparus flaviceps) - HBW 13, p. 74

Taxonomy: Aegithalus [sic] flaviceps Sundevall, 1850, “California” = Baja California, Mexico.
Relationships uncertain. Has been placed with the tits and chickadees (Paridae) and in the past even with the previously monotypic Bananaquit (Coerebidae); results of research on DNA-DNA hybridization, however, suggest affinities with the New World gnatcatchers and gnatwrens (Polioptilidae), rather than with any other group. Nevertheless, this species does share a number of features with the penduline-tits, in particular nest details, vocalizations, bill shape and incomplete post-juvenile moult; pending further research, it is considered better retained in present family. Geographical variation confusing, and somewhat clinal, with several races intergrading; number of races could potentially be reduced following taxonomic review. Birds of this species in SW New Mexico (SW USA) and C Durango (NC Mexico) of uncertain race, provisionally included in acaciarum. Proposed race fraterculus (described from Chinobampo, in south Sonora, in Mexico) is synonymized with nominate. Six subspecies currently recognized.