Robin party of 7, your birdbath is ready

This morning about a million birds decided to grace the old maple tree in our front yard, something that always makes me happy to see and hear, and which I encourage by trying to keep the nearby birdbath full when the temperature is above freezing. Almost immediately after I filled it this morning (with the claw-tingling mixture of ice chunks and freezing water that came out of the hose), everyone in the tree descended into it. Mostly they were robins, as you can see (picture taken through the window so as not to disturb them). Some days they are joined by sparrows, catbirds, mourning doves, or an occasional woodpecker or finch, but the robins are pretty feisty about keeping the party a robins-only affair. Their interactions are always fun to watch; today is the first day I've successfully caught this particular one on camera ():

Update 2/18/08: Ok, now I am forced to admit how dumb it was to keep the birdbath outside over the winter. My friend Diane, who has been known to go out and wrap every delicate thing in the yard when frost is forecast, warned me that this was not a good idea, but out of inertia and love of seeing birds in it, I left it out anyway. But after taking the picture above yesterday, I watched the water drain away (the poor robins kept coming back and trying to drink the dregs anyway) and realized there is a big crack in the basin. The birdbath is made of some kind of plastic resin and I'm trying to figure out what to plug the crack with that won't hurt the birds. Caulk has all sorts of gross stuff (phthalate esters, ethylene glycol, etc that are, according to the package "known by the State of California to cause cancer and birth defects"), so that seems like a bad solution, even though I live in Maryland which apparently remains blissfully unaware of these dangers. If anyone has ideas, I'd appreciate hearing them. I'm about to go chew up a pack of gum and stuff that in the cracks for lack of a better idea. Hope they like wintergreen.