Bushtit (Psaltriparus minimus) - HBW 13, p. 99

Taxonomy: Parus minimus J. K. Townsend, 1837, Columbia River, Washington State, USA.
Geographical variation complex. Races divisible into three groups, “nominate group” (including also saturatus, melanurus, californicus and grindae) of Pacific coastal regions, “plumbeus group” (with single race) in interior, and “melanotis group” (including also dimorphicus, iulus and personatus) in S of range; groups meet in zones of secondary intergradation in S USA (California, Texas) and N Mexico, and were for many years treated as representing two or three separate species on basis largely of theory that “melanotis group” and “plumbeus group” overlap without interbreeding in SW Texas, whereas these two groups display a near-continuous gradation of characters from N to S. Proposed race lloydi (described from Limpia Canyon, near Fort Davis, in Texas) represents a hybrid population between plumbeus and “melanotis group” found in USA-Mexico border region (extreme SW New Mexico and adjacent NE Sonora and NW Chihuahua, and C & W Texas). Otherwise, in California, plumbeus intergrades with race californicus (in “nominate group”) on E flank of Sierra Nevada and nominate race intergrades with californicus in E. Birds of this species in NE San Luis Potosí (C Mexico) of uncertain racial affinity, provisionally placed in iulus. Ten subspecies recognized.