I use a D300 with various lenses for bird photography up to ISO800 and even 1600 on occasion without problems with noise. I agree with the first answer that underexposure is the main cause of excessive noise. I dial in +1 eV exposure compensation on matrix measuring mode as default and check that I just don't blow the highlights, adjusting the compensation as necessary. If it is a particularly dark bird in difficult conditions I may even dial in +2 eV compensation. I shoot NEF/RAW only and adjust exposure as first step during post processing. I tried using the auto-ISO function on my D300 and D3 but did not like the results and have stopped doing so.