Birdflight is my favourite video. Unless I can handhold at least 10 seconds sharp birdflight with 5D2 I'll have to try V1 or similar and stick to 40D for stills. I only shoot in good light outdoors.

I do appreciate that lots of lovely bird action can be studied when the birds are perched but flight, especially of bigger birds, is too graceful to ignore just because it's tricky to get ... my XM2 (GL2) has been getting handheld snippets for years.

I've checked out several videos and a few reviews of 5D Mk II and I've seen or read nothing to suggest that the 5D2 has a video-future without a tripod.
I'm fairly sure it's a no-no for birdflight, apart from long-distance vistas of incoming flocks.