OCWD Online - least Bell's Vireo

The least Bell's vireo, Vireo bellii pusillus, is a federally listed endangered species sensitive to changes in riparian vegetation. Preferred habitat for this species is dense willow-dominated riparian habitat with lush understory vegetation that is in high quality 5 - 10 year-old early succession stage.

The least Bell's vireo is predominately an insectivore. During the early and mid portion of the nesting season most foraging occurs in the vicinity of the nest site, predominately in willow, Salix spp., Both high and low shrub layers are used as foraging substrate. These birds use non-riparian habitats occasionally and will travel an average of 15m to forage. Birds using non-riparian areas for foraging tend to have territories in the narrowest sections of riparian habitat.

A low, dense shrub layer is considered essential for nesting , and a large degree of vertical stratification is preferred. Willow are the most commonly used vegetation for this need. Plant species used for nesting and foraging include the California wild rose, Rosa california, and coastal live oak, Quercus agrifolia. Most nest sites are located near the edges of thickets. Nest height on average is 1m above the ground . Males are site tenacious and return to the same site to nest in succeeding years. Average territory size is about 0.8ha.