When the breeding season ends, Cassin’s Vireos join the flocks of other woodland birds for more protection before migrating with their young.

Prior to nest-building with a female, males perform courtship displays by ruffling their feathers and revealing potential nest materials.

The pair builds a well-crafted cup shaped nest made of bark strips, grass, and other fibers, suspended in the fork of a branch, and often decorated with lichen.

Despite challenges like parasitism by Brown-headed Cowbirds, which can reduce the overall nesting success, Cassin’s vireo populations have remained stable, even increased in some regions.

It is now placed in the genus Vireo, which includes small, insect-eating songbirds.The species is named after John Cassin, a popular nineteenth-century ornithologist.

The US Fish and Wildlife Service recognizes the two following subspecies: The Cassin’s Vireo’s diet consists of insects including true bugs, caterpillars, spiders, and ants.

[3] Brood parasitism by Brown-headed Cowbirds has been attributed to its recent population decline and rarity in areas like San Diego County.