Golden-crowned Kinglet Regulus satrapa
     Eastern   R. s. satrapa
     Western   R. s. olivaceus group

Blue-gray Gnatcatcher Polioptila caerulea
     Eastern   P. c. caerulea
     Western   P.c. obscura
Two subspecies differ slightly in plumage and voice. Nesting habitat preferences seem to differ but may simply be related to habitat availability. Breeding range does not overlap. Differences in voice and nesting habitat deserve more study.

Black-tailed Gnatcatcher Polioptila melanura
     Eastern   P. m. melanura
     Western    P. m. lucida
These two subspecies differ slightly in plumage and do not overlap in range, but a careful study (Atwood) found no other differences between them. 

Northern Wheatear Oenanthe oenanthe
     Greenland   O. o. leucorhoa
     Alaskan   O. o. oenanthe

Eastern Bluebird    Sialia sialis
     Northern   S. s. sialis group
     Arizona   S. s. fulva group

Veery Catharus fuscescens
     Eastern   C. f. fuliginosa group
     Western   C. f. salicicola
All variation is rather slight. There is subtle variation in color throughout the east, with slightly duller subspecies in the far northeast (Atlantic Canada) and in the Appalachians, but the drabbest overall is the western subspecies. Occasional individuals with much drabber plumage apparently occur in the far west, but the significance of these birds is unknown.

Gray-cheeked Thrush Catharus minimus
     Typical   C. m. aliciae
     Newfoundland   C. m. minimus

Swainson's Thrush Catharus ustulatus
     Pacific   C. u. ustulatus group
     Taiga/Interior West   C. u. swainsoni group

Hermit Thrush Catharus guttatus
     Taiga/Eastern   C. g. faxoni group
     Rocky Mountains   C. g. auduboni group
     Pacific    C. g. guttatus group

American Robin Turdus migratorius
     Eastern   T. m. migratorius group
     Black-backed  T. m. nigrideus
     Western    T. m. propinquus group

Wrentit Chamaea fasciata
Variation is clinal, with the darkest subspecies in the far northwest of range C. f. phaea, and palest in far southeast C. f. henshawi.

Brown Thrasher Toxostoma rufum
     Western
     Eastern

Curve-billed Thrasher Toxostoma curvirostre
     Arizona
     Texas
 
 American Pipit Anthus rubescens
     Arctic rubescens/pacificus
     Rocky Mountain  alticolus
     Asian japonicus

Loggerhead Shrike Lanius ludovicianus
     Lighter
     Darker Southern California
     San Clemente Island

Black-whiskered Vireo  Vireo altiloquus
     Florida
     Caribbean

Bell's Vireo Vireo bellii
     Eastern
     Arizona
     California (Least)

Blue-headed Vireo Vireo solitarius
     Northern  solitarius
     Appalachian  alticola

Hutton's Vireo Vireo huttoni
     Pacific
     Mexican

Warbling Vireo Vireo gilvus
     Eastern
     Western

Northern Parula   Parula americana
     Eastern 
     Western

Orange-crowned Warbler Vermivora celata
     Pacific  lutescens
     Taiga  celata
     Interior West  orestera
     Channel Islands  sordida

Nashville Warbler Vermivora ruficapilla
     Eastern
     Western

Yellow Warbler Dendroica petechia
     Northern group
     Eastern
     Sonorana
     Northern
     Golden

Black-throated Blue Warbler Dendroica caerulescens
     Northern 
     Appalachian

Yellow-rumped Warbler Dendroica coronata
     Myrtle
     Audubon's

Yellow-throated Warbler Dendroica dominica
     Southeast  dominica
     Interior East  albilora

Palm Warbler Dendroica palmarum
     Yellow (Eastern)
     Brown (Western)

Common Yellowthroat Geothlypis trichas
     Eastern group
     Western Group
     Pacific
     Interior West
     Southwest

Wilson's Warbler Wilsonia pusilla
     Taiga
     Interior West
     Pacific

Rufous-capped Warbler Basileuterus rufifrons
     Eastern
     Western

Yellow-breasted Chat Icteria virens
     Eastern
     Western