American Bushtit (Psaltriparus minimus)

Geographical variation complex. Races divisible into three groups, “minimus group” of Pacific coastal regions, single-taxon “plumbeus group” in interior, and “melanotis group” 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 two or three separate species in belief 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; nonetheless, considerable genetic differentiation of plumbeus revealed in recent general analysis of family#R, and further molecular work desirable. No clear vocal differences#R. Proposed race lloydi (described from Limpia Canyon, near Fort Davis, 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 “minimus 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.