Flash settings for birds in flight?

Hi Guys.Just got a flash(Sigma EF-610 DG Super) for bird photography to take photo's in overcast,harsh lighting conditions.I want to use my flash for birds in flight too,but don't know where to start.Help please.I reckon I should start with High Speed Sync to get higher shutter speeds but where from there?

Should I put my 50D on Manual and adjust from there or the normal AV(Avian)I normally use?Would my flash be able to keep up if I shoot a burst?And what settings do I set on my flash?ETTL and High Speed Sync with some flash exposure compensation?

Can I set my flash on High Speed Sync for perched birds too?And be ready and set for take-off shots?What distance would I get using High Speed Sync with a flash extender?Sorry asking all this maybe dumb questions.But I am a real beginner using flash..

Yes - you can certainly use high speed synch (and ETTL mode). You will usually be using the flash as fill only and will want to dial down the flash's exposure compensation - I'm probably most often down in the -1 2/3 to -3 range (but not always) - you will have to make a judgement call based on the available light and the situation.

The flash probably won't be able to keep up with a burst of shots without an external battery pack supplementing power. I am not familiar with the Sigma flash - is there a port to connect an external battery pack?. I have no idea what Sigma offers OEM, but as long as there is an external port you will likely at least have the option of a Quantum battery or something similar.

The distance you get from your flash extender will be dependent upon the power / guide number of the flash itself and the ambient light level in which you are shooting. Most manufacturers of fresnel lens type extenders claim a benefit of 2 to 3 stops, so you will have to do your own math for a given shooting situation based on that.

Thanks Jeff.Is the settings u describe for bif or perched birds?No Jeff the Sigma does not have an external port to connect an external battery.A shame really..How heavy on batteries is High Speed Sync?
Haven't really tested it so much thus far.

The Sigma's guide number is 61m at 105mm ISO 100 so I am really curious how far it will reach with the better beamer using HSS.If a subject is further off do I just adjust my flash's Exposure Compensation to 0 or +1 or so still using HSS?