Which Nikon DSLR is good for bird photography

Depends what kind of shots you're going to do.  If you're just taking shots of perched birds, most any Nikon will work just fine.  However, if you're taking shots of birds in flight, you'll probably want an auto-focus system at least as capable at the D7000, or a used D300/D300s.

For lenses, you'll want some reach.  The Nikon 70-300 VR is kind of the staple.  I've heard good things about the equivalent Tamron, but I haven't used one.  However, even 300mm is often not enough.  If you REALLY want some reach (and have the budget), there are a number of great long (and very expensive) Nikons, or you could look at the Bigma (Sigma 50-500 OS).  I consider it the best value out there, when you need some reach.  Most of the wildlife shots in my gallery were taken with it.  Be aware, it's a big, heavy lens.  Some examples: