If a tree on your street is suddenly full of sleek, crested birds, the waxwings are back. Bohemian waxwings spend the summer spread out through the northern forest, eating insects. When the cold comes they switch to fruit and travel in flocks, sometimes hundreds of birds at a time, going wherever the berries are. That's why they show up in town, where the streets are planted with mountain ash and crabapple. A flock lands on one tree, eats until the fruit is gone and moves on to the next. One bird can swallow several hundred berries in a day, which is more than twice its own weight. "Bohemian" is for the way they wander. "Waxwing" is for the small red tips on the wing feathers, which look like drops of sealing wax. They don't keep a schedule, so a tree that was full of them yesterday can be empty today. Listen for a thin, high trill from the top of a tree, then look up.