The Yellow-rumped Warbler is the toughest warbler in North America — the only one that regularly winters in Canada, surviving cold months that send every other warbler species to the tropics. Their secret is a unique ability to digest waxy berries (like bayberry and juniper) that other warblers can't process, giving them a winter food source no competitor can touch. They're handsome birds with slate-blue plumage, a bright yellow rump patch, and yellow flashes on their flanks and crown. At feeders they're one of the few warblers you'll ever see, visiting suet cages and platform feeders for high-fat fuel during cold weather. Their distinctive 'check' call note from dense shrubs often gives them away before you spot them.