What price range?
A Sony A7S has great low light if you need it, add a zoom lens and a variable ND for sunny days and that's the kit I'd suggest. Also, would suggest a Manfrotto monopod with 701 fluid head to give the necessary stability at range.
The 4k will assist in the edit afterwards because you can zoom in a little further.
However, all this costs £2k GBP so what's the budget?
Alternatively, maybe worth asking someone who films to come by and help you out. Maybe someone here would be happy to shoot and cut a little montage for you as I'm sure many people would be interested in seeing a crow flying around and coming back to you.
"80% of success is turning up" - Woody Allen