Good to see someone else on here from Utah.
To your question. Shooting any average sized bird with a 50 mm lens is going to be too far away on either a crop sensor or a full frame. And lets say you have good glass, light, and good technique to get the best shot ever taken by a camera. At 30 to 50 yards that you have mentioned, cropping down to that average sized bird will have no use other than just a smallish web image - not enough image left for a quality print.
There is no getting away from needing zoom for birds.
For landscape and night photography full frame is the way to go.
As I see it, what seems to rise to the surface is... First, a full frame camera. Second, a fifty or wider lens for your landscape photography. Third, a 70-300mm maybe with a small 1.4 Nikon teleconvertor and stealthy skills to sneak up on the birds.
From what you have described I see no other way around needing two lenses to accomplish your goals.
Welcome to the forum.