These are really different "animals" Paolo. I've used a 1D mkIII for gannets in flight and it was fantastic (have a D300 at work). It's by far the fastest of the bodies you mention and I would say this is your main concern. Also it has nice fat sensor sites (1.3 crop factor at 10 mp) so image quality is superb. The Canon is about 3x more expensive than the D300 so you will pay a price for these features.
If you don't have long glass yet you had better check pout the prices of Canon and Nikon 500 and 600 lenses. Canon is far less $$ for the same quality. You can also get them while Nikon long glass is very hard to get.