This bird was named by Audubon for John Graham Bell, who accompanied him on his trip up the Missouri River in the 1840s.

), mulefat (Baccharis glutinosa), California wild rose (Rosa californica), mugwort (Artemisia douglasiana), Fremont cottonwood (Populus fremontii), and Western poison oak (Toxicodendron diversilobum) shrubs or vines as nesting locations.

[4][5] Historically, the least Bell's vireo was a common to locally abundant species in lowland riparian habitat, ranging from coastal southern California through the Sacramento and San Joaquin Valleys as far north as Red Bluff in Tehama County.

In the decade since listing, least Bell's vireo numbers have increased six-fold, and the species is expanding into its historic range.

[6] Roughly half of the current least Bell's vireo population occurs on drainages within Marine Corps Base Camp Pendleton in San Diego County, particularly in the lower Santa Margarita River.