The Nature Conservancy blog Cool Green Science attempts to answer the question Why Do Birds Bathe? Although there are only a few studies the best guess is
Although the functions of bird bathing aren’t clearly known at this point, these studies suggest that bathing plays an important role in feather maintenance.
Read article at Splish, Splash: Why Do Birds Take a Bath? | Cool Green Science.
Natural History Wanderings 
Maybe for the same reason I take a bath: It feels sooooooooo good…….LOL
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By: Russel Ray Photos on May 7, 2015
at 7:59 AM
No studies are needed. A wildlife rehabilitator will tell you, from observation, that birds take baths so that they can preen their feathers. Feathers are essential to maintain the bird’s temperature control.
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By: sharonstjoan on May 5, 2015
at 10:17 PM