Nearly all birds bath frequently in water to keep their feathers in good condition and during the summer, bathing in water also helps the bird to keep cool.
Once in the water, the bird fluffs its feathers to expose the skin, submerges its belly and breast in the water, rolls back and forth by dipping its head into the water and creates a shower by flicking its wings. When finished, the bird shakes off the excess water and then flies off somewhere to dry and preen.
In our backyard it has been especially dry due to lack of rain, so when the bird bath is full of water, there is a line of birds ready for a bath and a drink! Here is a video I made this afternoon of the activity at the bird bath. In it you will see: Brown-headed Nuthatch, Carolina Wrens, Brown Thrashers, Northern Mockingbirds, House Finches, Northern Cardinals, and Chipping Sparrows.
For information about bird baths and to learn about creating a backyard habitat for wildlife see:
http://www.audubon.org/bird/at_home/pdf/GFLchap3.pdf
