Just about all flash for bird photography is done where the flash is coming from the same direction as the camera. This can produce some nice results, such as the image in this thread demonstrate, but it doesn't reach it's lighting potential.
Using the flash from a different position than the camera can give the bird more definition, produce sharper results, add drama, and can even have the effect of being softer light if you position the flash closer to the bird. Remember that with smaller light sources like a speedlight, the farther away from the subject you are - the harder the effect will be.
Some examples:
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On the woodpecker I even bounced the flash off an umbrella from a short distance to the Downy.