Ah, well luckily I don't bird so I wouldn't really need it. I think I would invest in a set of AB's over a flash.
You don't HAVE to use a 580ex for birding. The 430s will do plenty fine with a beamer. I think the 580's have 50% more power, but that doesn't mean a great deal unless you're using an 800mm. 430s don't have a port for battery packs though 





