Sparrows in dry mud.

[Sozzie]

Why do sparrows bath in dry mud ?

[Catso]

More usually known as a dust-bath. All birds do it, if they can find some nice dust!

It is to clean themselves. It's supposed to get rid of parasites (though I admit, that sounds a bit doubtful!).

[heathfield]

Here's a good site with an explanation: http://www.stanford.edu/group/stanfordbirds/text/essays/Bathing_and_Dusting.html

[Cetti]

Yes, it is to get rid of parasites Sozzie.

Some birds like the Blackbird, Jay etc have an even more unusual way of ridding themselves of harmful and itchy bugs. They disturb an ants nest on purpose causing them to crawl all over the bird. The birds then sit still, wings out in a spirit of ecstasy as the formic acid from the ants destroys the parasites. Clever, eh?

[WendyS]

All birds tend to suffer from fleas or other parasites and dusting themselves with dry soil is a good way of ridding themselves of them. The dusty feathers make an univiting environment for them. Sparrows especially love to find a dry finely hoed patch of soil on a summer day for a dust bath.