Turns out the mockingbird spends quite a bit of time visiting the heated bird bath! While I do see the occasional other bird drinking, it's usually the mockingbird taking a leisurely sip. I kinda like seeing him (her?) out there, drinking away, watching what's going on around but not seeming totally panicky like some birds do. And it's cute because he often seems very puffy, perhaps fluffing the feathers to retain warmth.