Cassins Vireo Vireo cassinii Xantus de Vesey       Field Guide IDs: NG-308; G-262; PE-228; PW-pl 49; AE-pl 450; AW-pl 516; AM(III)-100 Nest Location Nest Type Eggs & Mating System Dev. & Parental Care Primary & 2ndary Diet.. Foraging Strategy MF I: 14? DAYS ALTRICIAL 4 feet - 30 feet MF 4 (3-5) MONOG F: 14? DAYS MF HAWKS HOVER & GLEAN BREEDING: Coniferous-deciduous woodland. Occ 2 broods. DISPLAYS: Courting male fluffs conspicuous yellow flank feathers while bobbing, bowing, and singing to female. Male performs nest-building display while slightly crouched with body horizontal, usu without nest material in bill. NEST: Usu in conifer tree (in e) or in oak (in w); well made, basketlike deep cup, suspended by rim from prongs of forked twig, usu rounded, of grass, forbs, shredded bark, plant fibers, spider web, cocoons, decorated with lichen, lined with fine grass, hair. Male selects site. EGGS: White, spotted with browns, black, esp near large end. 0.8" (20 mm). DIET: Almost entirely insects; fleshy fruits compose 25% of diet in January, but only 4% year-round. CONSERVATION: Winters s to Costa Rica, Cuba. Common cowbird host; if cowbird egg laid first, often builds second floor of nest to cover it. NOTES: Males occ start building one or more nests before pairing. Fearless around nest; female is a close sitter. Parents divide fledged brood and leave nest area. Recent studies indicated w and e populations two separate species. Formerly known as Solitary Vireo. STANFORD. NOTES: ESSAYS: Decline of Eastern Songbirds; Cowbirds; Species and Speciation; Parental Care. REFERENCES: James, 1978; Martindale, 1980.