The Orange-crowned Warbler, Oreothlypis celata, breeds widely over much of western and northern North America, and east across Canada. Authorities recognize four subspecies, which differ to varying extents in their plumage, molt patterns, breeding distributions, and migratory routes, among other things. This species prefers habitats with shrubs and low vegetation, often in patchy oak or aspen forest, or in riparian areas or chaparral. Wooded habitat provides suitable conditions for the warbler's nest, placed on or near the ground. Like other members of its genus, the Orange-crown gleans insects from leaves, blossoms, and the tips of boughs, but it also eats some berries and fruit and is attracted to suet in winter. Where Red-naped sapsuckers (Sphyrapicus nuchalis) drill holes in tree trunks, this warbler often is the most common species to feed at the sap wells.
This species is often numerous in suitable habitat, and may be the most abundant breeding paruline in some areas. Its song is highly variable, and many individuals can be separated by their distinctive song patterns. Most populations are strongly migratory, although members of the sordida race breeding along and off the California coast may move only short distances in fall and winter.
The Orange-crowned Warbler has been the subject of extensive studies of its molt, pterylography, and ecto-parasitism (Foster 1967a, Foster 1967b; Foster 1969a). Much past information on the species' ecology, behavior, and breeding, however, has been anecdotal. Within the past two decades more comprehensive studies have been made, especially of O. c. lutescens in Contra Costa Co., central California (Gilbert Gilbert 1986, Gilbert 1994, WMG), O. c. orestera on the Mogollon Rim in central Arizona (Zyskowski 1993, Martin and Martin Martin and Martin 2001b, Martin and Martin 2001a; Martin 2007c), and of O. c. sordida on the Channel Islands off s. California (C. Ghalambor and S. Sillett, pers. comm.; Peluc et al. 2008; and M. Sogge and C. van Riper III). Throughout this revised account much unpublished information is attributable to M. Sogge and C. van Riper III, two co-authors of the original 1994 account; this information is referenced as MKS and CvR.