"Yellow" subspecies of Palm Warbler photographed in NH in fall
"Western" subspecies of Palm Warbler photographed in winter on Sanibel Island, on the west coast of southern FLIn addition to many sparrows such as White-throated, White-crowned, Song, Chipping, Swamp, and Lincoln's Sparrows we had migrating through New England, there are some Palm Warblers, top photo above. These late migrating, beautiful warblers have yellow breasts and deep yellow undertail coverts. They constantly wag their tail up and down, a nice giveaway to their identification. These bright "yellow" Palms are the eastern subspecies of Palm Warbler (Dendroica palmarum hypochrysea) and breed from central Quebec east. They winter along the Gulf Coast, from LA to northern FL.
The "western" subspecies of Palm Warbler (Dendroica palmarum palmarum) breeds from Ontario west, across to parts of the Yukon and ne. British Columbia and winters in the Southeast, down through south FL. Some may also winter on the West Coast. This subspecies has very little yellow on the breast but still has bright yellow undertail coverts. There is a breeding zone south of James Bay where they intergrade. This gives you some idea of why Palm Warblers may look different, depending on which area of the country you are in.
Enjoy watching the Palm Warblers forage near the ground in goldenrods along the edges of fields in migration.
For more on the subspecies of Palm Warbler as well as how to identify fall warblers, see The Stokes Field Guide to the Birds of North America, the best-selling photographic field guide available.