The stout bill of the Yellow-rumped warbler is adapted for eating both insects and berries. The ability to use fruit as a food source allows the Yellow-rumped Warbler to winter further north than those warblers dependent only on insects.
1. Sibley DA. The Sibley Guide to Birds. Alfred A. Knopf New York. 2000.
2. Sibley DA. The Sibley Guide to Bird Life & Behaviour. Alfred A. Knopf New York. 2001.