The Tree Swallow is able to winter far north of its relatives primarily due to its ability to supplement its diet of insects with seeds and berries. In the Mid-Atlantic, a staple of its winter diet is bayberry and Wax Myrtle fruit. The same dietary supplement also fuels the hordes of Yellow-rumped "Myrtle" Warblers that winter on Assateague Island, far north of other insect-eating warblers.