Vireo bellii Aububon, 1844
Basis for Listing
Bell’s Vireo (Vireo bellii) is a bird of brushy thickets and riparian areas in the Southwest, Central Plains, and Midwest regions of the United States. It is generally rare and quite locally distributed in southern Minnesota, which lies at the northern edge of its breeding range
Bell’s Vireo requires dense and shrubby thickets adjacent to grassland or sedge/grass wetlands. This microhabitat may occur in a variety of broader habitat settings. Shrubby edges that seem like suitable habitat are quite common and widespread in much of Minnesota, yet Bell’s Vireo is found in only a tiny proportion of such areas.
Bell’s Vireo has been reported from approximately 50 locations in Minnesota; however, it is consistently found at fewer than ten of these sites. Significant regional declines have been detected, with federal breeding bird survey (BBS) routes in the Midwest showing an average population decline of 2.9% per year between 1966 and 2007. However, in Minnesota, relatively few BBS routes are located within this species' normal breeding range, and there may be little suitable Bell’s Vireo habitat along these routes. Due to its rarity, patchy distribution, and specific habitat needs, Vireo bellii was listed as a species of special concern in 2013.
Bell’s Vireo is a rather non-descript sparrow-sized songbird, with olive-green upperparts and whitish underparts accentuated by a yellowish wash on the flanks. This species has indistinct white “spectacles” and faint white wing-bars. Due to its secretive nature, Bell’s Vireo is best detected and identified by its distinctive song, a somewhat wheezy series of phrases alternatively rising and falling in pitch. Bell’s Vireo can be confused with other vireos, warblers, and small flycatchers. Most similar to other vireos, it can occur in similar habitat to the White-eyed Vireo (Vireo griseus), which is very rare in Minnesota. The White-eyed Vireo has a distinct white eye (iris), bolder yellow spectacles, and brighter more extensive yellow flanks. The relatively common Warbling Vireo (Vireo gilvus) is more often found in trees, rather than shrubs, has a white eyebrow, rather than spectacles, lacks wing-bars, and has little to no yellow wash on its underparts.
In Minnesota, Bell’s Vireo prefers shrub thickets, clumps, and edges within or bordering open habitats such as grasslands or wetlands. Occasionally it may occupy more extensive shrublands, either upland or wetland. In wetland situations, suitable herbaceous vegetation is typically dominated by sedges or grasses, rather than cattails. Shrub species most often associated with Bell’s Vireo are various species of willow (Salix sp.), dogwood (Cornus sp), particularly gray and red-osier, and wild plum (Prunus americana).
The majority of Bell’s Vireo records in Minnesota come from habitats not considered to be native plant communities, primarily old fields with brushy edges. To be considered a Native Plant Community certain criteria must be met, including minimal disturbance by humans, minimal exotic species present, as well as certain size limits (extent of habitat). The shrubby edges and thickets that Bell’s Vireo requires often do not meet these requirements. In cases where Bell’s Vireos have been found in recognized native plant communities, the most important seem to be seepage meadow/carr, mesic prairie, and dry prairie. They have also been found in wet seepage prairie and calcareous fen.
Biology / Life History
Bell’s Vireo is a long-distance migrant, wintering in Mexico and Central America. Breeding Season begins in early June, and most young are out of the nest by July. It builds its nest in a shrub, typically 0.3 – 1.0 m (1-6 ft.) off the ground. Like most vireos, the nest is a cup suspended from a forked branch. Usually there are four eggs, incubated by both the female and male. Young typically hatch after 14 days, are fed by both adults, and fledge about 14 days later. Elsewhere in their breeding range, Bell’s Vireos are commonly parasitized by Brown-headed Cowbirds (Molothrus ater); however, this has rarely been documented in Minnesota. Primarily insectivores, Bell’s Vireo gleans insects, spiders, and other arthropods from foliage.
Conservation / Management
In Minnesota, there is no strong evidence that habitat is a limiting factor for the presence of Bell’s Vireo, since much apparently suitable habitat is unoccupied. Certainly available habitat has been greatly reduced from historic levels by land use changes, such as conversion to agriculture or urban/residential development; however, active habitat management for this species is probably not warranted at this time.
Grassland and shrub habitats in areas where Bell’s Vireo is known to occur should be maintained with several important considerations. Invasive species that may compromise the bird’s habitat, particularly reed-canary grass (Phalaris arundinacea), hybrid/narrowleaf cattail (Typha X glauca), purple loosestrife (Lythrum salicaria), and buckthorn (Rhamnus cathartica) should be controlled. At known Bell’s Vireo sites, provision must be made for maintaining shrub patches in native prairies otherwise managed to control or eliminate woody cover. Prescribed burning needs to be conducted such that adequate shrub patches are maintained or enhanced. Longer burn rotations or protection of shrub patches may be necessary. Grazing should be closely monitored or limited in known Bell’s Vireo habitat so as not to reduce necessary herbaceous cover in proximity to shrub patches. Shrubby ecotones between forests and open grasslands/wetlands need to be maintained or enhanced.
Conservation Efforts in Minnesota
The breeding distribution and population status of this small songbird is not well known compared with many other Minnesota bird species. As a result, conservation efforts for Bell’s Vireo have been limited to inventories seeking to learn more about the breeding distribution of this species in the state. The Minnesota Department of Natural Resources’ Minnesota Biological Survey has conducted targeted searches of potential Bell’s Vireo habitat resulting in the documentation of this species at several new locations. Additional records of this species have been found during the Minnesota Breeding Bird Atlas.
Steven P. Stucker (MNDNR), 2018
(Note: all content ©MNDNR)