Best lens combination for birding?

I'm an ameteur bird photographer and am planning to buy the nikon d7200 for birding. But i'm stuck on which lens to buy. I've got 3 options.
1. Buy the tamron sp 150 600mm lens
2. Buy the nikon 70 300mm lens with a good teleconverter.
3. Get a spotting scope.

The reason for the confusion is i don't know which one will give me the best results… If you r suggesting option 2 or 3 please tell which teleconverter or spotting scope i should use?

This link will help in determining which one may be best for your needs: http://www.photozone.de/...lens-tests

I would assume a spotting scope is fine still objects, but I've never seen a successful bird image taken with one.

To see how these lenses perform out in the real world, you can go to 500px.com and do a search for the specific lens. I'd also do a search for birds to see what's being used.

To get serious with bird pictures 300mm is rarely adequate.
I took these pictures of ravens in Yellowknife with my 18-200mm at 200mm. Not bad, but it is a pretty big bird, and the ravens in Yellowknife, although not tame, are not very shy. This is about the closest I could get.

Cameralabs looked at a few stronger telephotos here:
http://www.cameralabs.com/reviews/Nikon_Nikkor_AF-S_200-500mm_f5-6E_ED_VR/

No teleconverter. They degrade picture quality too much. Simply buy the most number of mm you can afford then try to get as close to your target as possible.

Now, if you really don't mind picture quality at all, get a mirror lens with at least 500mm. They are very light and can be hand-held (although you might still prefer to use a tripod). The problem with them, besides their very poor optical quality is their fixed aperture size (f/8?) so you will have problems in low light. Reach however is amazing! Due to their price, treat them as toys.