Getting it "right" in camera has definite advantages and huge crops often degrade image quality.

I use cropping for creating a more pleasing composition and I suspect this is a very common practice but if it degrades the quality much I will either not crop it or delete it entirely.

With bird photography my goals are to get a good pose, good background as well as properly exposed and very sharp image in camera.

Extreme cropping is not an issue for most of my bird pictures because with my set up I have complete control of my distance to subject so I will not require a large crop.

In the field this is not always possible and in this situation it may be beneficial to have more megapixels or a longer lens or both!