Wilson's Warbler Cardellina pusilla Scientific name definitions

First described by naturalist Alexander Wilson, this wood-warbler is a familiar and characteristic species of wet habitats in the boreal and Pacific coastal zones. The most widespread in its genus, Wilson's Warbler breeds throughout Alaska, most of Canada, and south through the western United States to southern California and New Mexico, often the most abundant warbler in these regions. Distinguishable from similar species by its black cap, simple and bright color pattern, characteristic tail-waving, and short, chattering song, this species is quickly recognized darting through shrub willows and undergrowth. It nests on or near the ground at elevations ranging from sea level to the alpine zone. Breeding territories are usually located in riparian habitats or wet meadows with extensive deciduous shrub thickets.

Just as it breeds across a wide altitudinal and latitudinal range, Wilson's Warbler also winters in a great diversity of environments, ranging from the east to the west coast of Mexico and Central America, and from the Caribbean lowlands to the cloud forests of the continental divide. Moreover, it is the only migrant warbler regularly found in tropical high plains (paramo). In the winter, Wilson's Warbler shows a diversity of behavioral strategies, with many birds defending territories, others acting as winter “floaters,” and still others joining large mixed-species foraging flocks.

Breeding Wilson's Warblers are socially monogamous, but polygyny occurs and a high rate of extrapair paternity has been found in one population. Brood parasitism by Brown-headed Cowbirds is generally low, although it can be locally high in some areas. Extensive studies have addressed the species' breeding biology (Stewart 1973 Stewart, R. M. (1973). Breeding behavior and life history of the Wilson's Warbler. Wilson Bulletin 85:21-30. Close , Stewart et al. 1977 Stewart, R. M., R. P. Henderson and K. Darling. (1977). Breeding ecology of the Wilson's Warbler in the high Sierra Nevada, California. Living Bird 16:83-102. Close , Ammon 1995b Ammon, E. M. (1995). Reproductive strategies and factors determining nest success in subalpine ground-nesting passerines. Ph.D. dissertation, University of Colorado, Boulder, CO, USA. Close , R. Bereson, J. Rhymer, and R. C. Fleischer, unpubl., WMG), survivorship (Chase et al. 1997 Chase, M. K., N. Nur and G. R. Geupel. (1997). Survival, productivity, and abundance in a Wilson's Warbler population. Auk 114:354-366. Close ), migration (Yong et al. 1998 Yong, W., D. M. Finch, F. R. Moore and J. F. Kelly. (1998). Stopover ecology and habitat use of migratory Wilson's Warblers. Auk 115:829-842. Close ), and diet (Raley and Anderson 1990 Raley, C. M., and S. H. Anderson (1990). Availability and use of arthropod food resources by Wilson's Warbler and Lincoln's Sparrow in southeastern Wyoming. Condor 92:141–150. Close ), but many interesting aspects of its biology remain to be learned. For instance, geographic and altitudinal variation in life history traits, ecophysiology, mating system, extrapair paternity, and cowbird parasitism could be subject to comparative investigations. Also, the evolutionary ecology of above-ground vs. ground nesting Wilson's Warblers (Martin 1988c Martin, T. E. (1988c). Nest placement: implications for selected life-history traits, with special reference to clutch size. American Naturalist 132:900-910. Close ) and of Wilson's Warbler winter territoriality deserve additional study.

Long-term trend analysis indicate recent population declines, particularly in the western portion of the species' range; large-scale destruction of riparian habitat is likely a leading cause. These populations declines and their causes merit further investigation, since declines appear to have become more widespread in recent years.