I've been using when mourning doves slide into the water that it's time to refill and clean the bird bath. They're that predictably stupid. They try hopping from one foot to the other while flapping, and if they catch their balance and don't slide all the way in, they sit there looking confused about what just happened and just stare at the water instead of drinking again.
Edit to add visits from cardinals and blue jays. Many many more blue jays that I love seeing.
I've noticed that sometimes the blue jays scoop up as much water as possible by sliding their bills along the water before lifting their heads to drink. I'm starting to think they're one of the more intelligent birds.
