Vireos (Vireonidae Family)

Quail Ridge is inhabited by three sympatric species of vireos – the resident Hutton’s and the summer visiting Cassin’s and Warbling. All are similarly small, olive-colored birds with rounded heads and short bills. They all build cup nests near the ends of live tree branches or chaparral, and both sexes incubate the eggs. In addition, they all will join mixed-species flocks and expand their diets to include fruits in the winter.

The only non-migratory vireo in the western U.S., Hutton’s Vireo (Vireo huttonii) is typically a woodland resident but may disperse locally. This sedentary tendency has facilitated local divergence of the species – there are up to twelve subspecies – and is the result of an affinity for evergreen trees. The Pacific Hutton’s Vireo occupies the western half of California year-round. These birds forage in the middle to upper tree regions, actively gleaning insects and some arthropods from leaf surfaces.

Cassin’s Vireo (Vireo cassinii) formerly was considered one of nine subspecies of the Solitary Vireo (Vireo solitarius), until cytochromic⁹² and allozymic⁸⁹ testing substantiated its designation as a separate species in 1998⁷⁹. Cassin’s Vireos breed throughout most of California, with the exception of the Mojave Desert and Central Valley, and they are confirmed breeders at Quail Ridge. Although both females and males strongly defend their clutch of 3-5 (usually four) eggs, their nests are moderately susceptible to parasitism by Brown-headed Cowbirds (one nest at Quail was found to be parasitized). Cassin’s Vireo is a deliberate foliage gleaner.

Two of five subspecies of warbling vireos occupy the United States: a western form (Vireo gilvus swainsonii) and an eastern form (V. gilvus gilvus) that occasionally enters California. The western form breeds along the middle and northern California coast and in parts of the Sierra, and winters in southern California and Mexico. Although possible, it is unconfirmed as a breeder at Quail Ridge. To catch insects, warbling vireos will frequently employ hawking, stalking, and hovering in addition to gleaning. Although they prefer upper and middle strata, they will forage from just above the ground to near the top of the canopy. Warbling Vireos are frequently parasitized by Brown-headed Cowbirds; V. g. swainsonii is particularly susceptible because it has not developed the defense of puncturing and ejecting cowbird eggs like its eastern counterparts.

Species and Guild Accounts

Birds Page

Listen and identify birds at: http://identify.whatbird.com/mwg/_/0/attrs.aspx

Photo Credits: Title, California Quail (Joyce Gross), Hutton and Warbling Vireo photos (Will Turner) - for more of his bird pictures see: http://www.tucsonbirds.org/BirdIDCenter.asp. Cassin's Vireo photo (Peter LaTourrette) - for more of his bird pictures see: http://www.birdphotography.com/. For more pictures see: http://elib.cs.berkeley.edu/photos/browse_imgs/bird.html