Warbling Vireo (Vireo gilvus)

Photo by Dennis Malueg Warbling Vireo by Dennis MaluegWarbling Vireo distribution map

Status/Protection

Population Information

Federal BBS information can be obtained at http://www.mbr-pwrc.usgs.gov/bbs/bbs.html by clicking on Trend Estimates and selecting the species in question. All estimates are for 1966-2005.

Life History

Habitat Selection

Throughout their range, Warbling Vireos are strongly associated with mature mixed deciduous woodlands, especially in riparian areas (Gardali and Ballard 2000). In Wisconsin they inhabit a wide variety of habitat types, with more than 100 habitat codes described during the Wisconsin Breeding Bird Atlas (Harriman 2006). Overall habitat structure typically consists of large trees with a semi-open canopy, either in the forest interior or along edges and openings. Warbling Vireos are not considered to be area-sensitive and will nest in forest fragments and remnants of almost any size (Bent 1950, Gardali and Ballard 2000). Nests are often placed in the periphery of a shrub or tree, usually supported by two lateral limbs (Gardali and Ballard 2000). In Wisconsin, elm, maple, willow or poplar are common nest trees (Robbins 1991).

Habitat Availability

Although this species is largely a habitat generalist, habitat loss resulting from agricultural and urban expansion may have negative impacts. Southern Wisconsin forests have experienced significant loss and fragmentation since pre-settlement times (Mossman 1988, WDNR 1995). Current forest management practices, grazing, and invasive species have altered the composition and structure of remaining southern forests (WDNR 2005). However, it is not well-known how these changes affect Warbling Vireos.

Population Concerns

Population trends are variable across this species’ range. Breeding Bird Survey (BBS) data suggest a significant annual increase range-wide but a non-significant decline in Wisconsin (Sauer et al. 2005). It is considered a common summer resident and breeder throughout most of Wisconsin (Robbins 1991). During the six-year period of the Wisconsin Breeding Bird Atlas, observers recorded evidence of breeding in 69% of the surveyed quads (Harriman 2006).

Eastern populations of Warbling Vireo appear to be less frequently parasitized by Brown-headed Cowbirds compared to western populations (Sealy et al. 2000). No parasitism, for example, was found in 43 nests in studies from Michigan, Kansas, and Illinois (Sutton 1949, Johnston 1964, Graber et al. 1985). Nest depredation is a significant limiting factor in many western populations, but this is not well-studied for eastern populations. Habitat loss on the wintering grounds may be impacting this species (Gardali and Ballard 2000). Indiscriminate spraying to combat gypsy moth larva could adversely affect other caterpillar species, thus reducing available prey (Harriman 2006).

Recommended Management

Management efforts that protect tracts of mature deciduous forests, particularly riparian woodlands, will likely benefit this species. Within known breeding areas, managers should retain scattered large trees, particularly elm, maple, poplar, and willow. Warbling Vireos have shown positive responses to bottomland hardwood restoration in the southern U.S. (Twedt et al. 2002) and would likely benefit from similar efforts in Wisconsin. Areas with a high potential for restoration, such as young stands or small tracts of deciduous forest in southern Wisconsin, should be identified and considered for future restoration.  

Research Needs

Limiting factors on both the breeding and wintering grounds are poorly known. In Wisconsin, studies investigating nest depredation and brood parasitism rates within different habitat types may help to elucidate reasons for possible statewide decline. Although tolerant of edges and human-altered landscapes, reproductive success should be measured to determine the true suitability of these habitats.

Information Sources

References

Contact Information

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013.
The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.

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