Oh, it is probably quite real. 

Now, if someone was claiming that some birds on a set of wires had come out sounding exactly like Bach's Sinfonia from Cantata #29, then I would suspect a hoax.  Not that it would be impossible, mind you.  Just so highly unlikely (and requiring one heck of a lot of birds).

It probably took taking a few pics on different days to actually get something nice sounding.

For those who read and/or know a bit of theory though, notice that the person decided that birds only indicate notes that are the space above a line.  They are obviously using a G clef, and that would restrict the possible notes to F, A, C, E, G. 

So possible combinations of notes as chords would include F Major, A minor, C major, and some other useful combinations.  So it would be more likely to sound a bit "musical" than if the person had included the lines somehow, since a good number of unpleasant dissonances are avoided.

You wouldn't really need to look for birds either (though it is an element of fun, if you just happen to live near somewhere with 5 parallel lines they like to perch on like that).  You could just take a piece of score paper (or draw 5 lines) and close your eyes and make a bunch of dots with a pencil and use those to generate notes by the same "rules".  It is not at all unlikely you would come up with something that sounds at least as musical as those birds did, if you make a few tries.

Birds weren't mentioned as a writing tool back in composition class, but closing your eyes and making a bunch of dots and seeing if you can find any usable passages or ideas in it was. LOL

Hopefully that suggestion won't put too many birds out of work, though.. "Times is hard.."