Vireos (Vireonidae)

Cassin's Vireo (Vireo cassinii) - HBW 15, p. 425

French: Viréo de Cassin German: Cassinvireo Spanish: Vireo de Cassin
Other common names: Solitary Vireo (when treated as conspecific with V. plumbeus and V. solitarius)

Taxonomy: Vireo cassinii Xántus de Vesey, 1858, Fort Tejon, California, USA.
Probably forms a superspecies with V. plumbeus and V. solitarius; the three were formerly treated as conspecific, but molecular-genetic studies indicate that they merit treatment as separate species. Breeding range in W Canada overlaps slightly with that of V. solitarius, and some interbreeding may occur; cytochrome b sequence studies, however, indicate as much divergence between the two as between V. solitarius and V. flavifrons. Two subspecies recognized.

Subspecies and Distribution:

  • cassinii Xántus de Vesey, 1858 - breeds SW Canada (S British Columbia S from c. 53° N) and W USA (Washington and W Montana S to S California), disjunctly also in NW Mexico (mountains of N Baja California); migrates to W Mexico (S to Oaxaca).
  • lucasanus Brewster, 1891 - S Baja California (W Mexico).