From page 539 of The Warbler Guide:
A Yellow-rumped Warbler can be identified in flight by a numbers of features. It’s slight is bouncy and strongly tacking with irregular wing beats that are mostly below the body. It takes short glides, both open- and closed-winged and often mixes flight with chip calls. It is large, stocky, and hunchbacked with long blunt wings. Its color is overall gray with yellow shoulders, wing bars and rump.
The Warbler Guide
Tom Stephenson & Scott Whittle
Warblers are among the most challenging birds to identify. They exhibit an array of seasonal plumages and have distinctive yet oft-confused calls and songs. The Warbler Guide enables you to quickly identify any of the 56 species of warblers in the United States and Canada. This groundbreaking guide features more than 1,000 stunning color photos, extensive species accounts with multiple viewing angles, and an entirely new system of vocalization analysis that helps you distinguish songs and calls.
The Warbler Guide revolutionizes birdwatching, making warbler identification easier than ever before. For more information, please see the author videos on the Princeton University Press website.
Download the app here!