This species account is dedicated in honor of Ellen Adelson, member of the Cornell Lab of Ornithology's Administrative Board.
Editor's Note: Phylogenetic analyses of sequences of mitochondrial and nuclear DNA indicate that all species formerly placed in Dendroica, one species formerly placed in Wilsonia (citrina), and two species formerly placed in Parula (americana and pitiayumi) form a clade with the single species traditionally placed in Setophaga (ruticilla). The generic name Setophaga has priority for this clade. See the 52nd Supplement to the AOU Checklist of North American Birds for details. Future revisions of this account will reflect these changes.
A splash of yellow in a patch of willow. Aptly named, the Yellow Warbler is found throughout much of North America in habitats briefly categorized as wet, deciduous thickets. One common feature of Yellow Warbler habitat is the presence of various species of willows (Salix spp.), which dominate regions with high densities of Yellow Warblers, as in southern Canada, and regions where the species is sparse and local in distribution, as in the southwestern U.S. For populations of Yellow Warblers south of U.S. borders, mangroves are a dominant feature of their habitat.
The Yellow Warbler is the most strikingly yellow of North American wood-warblers. Yellow Warblers also have variable amounts of chestnut streaking on the breast, and southern forms have variable amounts of chestnut on the head. The streaking is usually more prominent in adult males and less so in females and immatures.
There is extensive morphological variation within this species, more so than within any other wood-warbler. Traditionally, the various subspecies of Yellow Warbler have been arranged into 3 groups, mainly based on the color of the head in adult males, and have been recognized in the past as distinct species (see Browning 1994 ), even though these groups may not reflect underlying evolutionary relationships: Yellow Warbler (aestiva group)—yellow-headed, migratory forms breeding in North America; Golden Warbler (petechia group)—largely chestnut-capped, resident forms in the West Indies; and Mangrove Warbler (erithachorides group)—chestnut-hooded, resident forms of coastal Middle and northern South America. Unless otherwise indicated, this account emphasizes the biology of the aestiva group, referred to simply as Yellow Warbler; Golden Warbler and Mangrove Warbler will identify separately those nonmigratory groups.
Abundant and widespread, having the broadest distribution of any Dendroica warbler, the Yellow Warbler has been a frequent subject of study. Research in southern Manitoba by Spencer G. Sealy and his students has examined the ecology and breeding biology of this species (e.g., Bierman and Sealy 1982 , Goossen and Sealy 1982 , Hobson and Sealy 1989c , Hébert and Sealy 1993a ) as well as interactions between Yellow Warblers and Brown-headed Cowbirds (e.g., Briskie et al. 1990 , Sealy Sealy 1992 , Sealy 1995 , Gill and Sealy 1996 , Gill et al. 1997 , McMaster and Sealy 1998 ). Further study in Ontario has examined warbler-cowbird interactions ( Clark and Robertson 1981 , Burgham and Picman 1989 , Scott and Lemon 1996 ) and relationships between reproductive success, paternal care, and male plumage (Studd and Robertson Studd and Robertson 1985a , Studd and Robertson 1987 , Studd and Robertson 1988 , Lozano and Lemon 1996 ).