They also eat berries, especially before migration and in winter quarters, where they are – like other vireos – apparently quite fond of gumbo-limbo seeds, though they will not venture into human-modified habitat to get them.

[3] They make a deep cup nest suspended from a tree branch or shrub, placed relatively high in the east and lower in the west.

Some authorities split the eastern and western races of this species into separate species: The western warbling vireo, V. swainsoni, includes V. g. swainsoni, which breeds from southeastern Alaska and southwestern Northwest Territories to the Sierra San Pedro Mártir, Baja California, and V. g. brewsteri, which breeds from southern Idaho, Wyoming, and Montana to south-central Oaxaca.

The swainsoni group also includes V. g. victoriae, an isolated population breeding in the Sierra de la Laguna, Baja California Sur, and migrating to unknown wintering grounds.

[4] The eastern warbling vireo, V. g. gilvus, breeds from central Alberta and northern Montana east and south through most of the United States and parts of southern Canada, outside the range of the previous group.