11 Ounce Size Silhouettes of popular North American wild birds disappear to reveal the birds in full color. Species include: Cardinal, Green Jay, Eastern Bluebird, Bullock’s Oriole, Blue Bunting, Red-Bellied Woodpecker, Lazuli Bunting, Goldfinch, Scarlet Tanager, Rose-breasted Grosbeak, Black-throated Blue Warbler, Painted Bunting and Housefinch! Wonder mugs are color-changing coffee mugs that change dramatically when a hot beverage is added. If you’re looking for a unique gift for them, what a unique way to remind them of you daily! These unique, high quality gift mugs utilize color-changing or “thermochromatic” ink that changes color when hot beverages are poured into the inside of the mug. Color change gift mugs are ideal for fund raisers, birthday gifts, teacher’s gifts, corporate gifts and more. All mugs are microwaveable.