Least Bell’s Vireo (Vireo bellii pusillus)

The least Bell’s vireo (LBVI) is a migratory songbird, dependent upon the riparian habitat for breeding. Least Bell’s vireo is 4 ¾ -5 inches in size, and is smaller than a sparrow. Its coloring is dull olive-gray above, whitish below, a faint white eye ring and fainter wing bars. The nesting is 3-5 white eggs, sparsely marked with brown in a well made pendant cup of plant down and bark stripes, placed in a dense tree or shrub.  

Once widespread and abundant throughout riparian woodlands in California  and northern Baja California, Mexico, the species has only recently began a revival on population numbers after a forty-year decline that nearly resulted in their extinction. Removal of riparian vegetation by farmers, flood control projects and water diversions, and lowered water tables due to groundwater pumping destroyed most of its’ habitat.  

The least Bell’s vireo numbers have increased in some areas thanks to collaborate efforts of various agencies to intensely manage riparian habitat, including the removal of nonnative vegetation and avian species. This bird is a federally listed endangered species. 

Information on federally-listed threatened and endangered species can be found at the U.S. Fish and Wildlife website at http://www.fws.gov/endangered/.  Information on State-listed threatened and endangered species can be found at the California Department of Fish and Game website at https://fgc.ca.gov/CESA.