My present DSLR is a D80, I moved up from the D70s not because anything was poor about the D70 but because their price fell sharply with the introduction of the D90. It was a bargain for the body only (£300).
It is almost identical to the D70(s), most of the controls are in the same places and the menu system is similar.
At 10M pixels, it gives (perhaps surprisingly) only slightly larger images in terms of linear dimensions.
It has better noise levels than the D70 for any given ISO speed, although not (reportedly) as good as the D90.
Is it any good for birding? Well, probably not with the standard lens unless you can get within a few feet of your target
